Stock-Based Compensation Plans (Details) (USD $)	12 Months Ended					12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended			12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended													12 Months Ended
Stock-Based Compensation Plans (Details) (USD $)	Dec. 31, 2011 plan	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2006 Two-Year Performance RSUs January 1, 2006 to December 31, 2007 performance period	Dec. 31, 2011 Two-Year Performance RSUs January 1, 2006 to December 31, 2007 performance period	Dec. 31, 2006 Two-Year Performance RSUs January 1, 2007 to December 31, 2008 performance period	Dec. 31, 2011 Two-Year Performance RSUs January 1, 2007 to December 31, 2008 performance period	Dec. 31, 2008 Two-Year Performance RSUs January 1, 2008 to December 31, 2009 performance period	Dec. 31, 2011 Two-Year Performance RSUs January 1, 2008 to December 31, 2009 performance period	Dec. 31, 2009 Two-Year Performance RSUs January 1, 2009 to December 31, 2010 performance period	Dec. 31, 2011 Two-Year Performance RSUs January 1, 2009 to December 31, 2010 performance period	Dec. 31, 2010 Two-Year Performance RSUs January 1, 2010 to December 31, 2011 performance period	Dec. 31, 2011 Two-Year Performance RSUs January 1, 2010 to December 31, 2011 performance period	Dec. 31, 2011 Three-Year Performance RSUs Y	Dec. 31, 2006 Three-Year Performance RSUs January 1, 2006 to December 31, 2008 performance period	Dec. 31, 2011 Three-Year Performance RSUs January 1, 2006 to December 31, 2008 performance period	Dec. 31, 2007 Three-Year Performance RSUs January 1, 2007 to December 31, 2009 performance period	Dec. 31, 2011 Three-Year Performance RSUs January 1, 2007 to December 31, 2009 performance period	Dec. 31, 2008 Three-Year Performance RSUs January 1, 2008 to December 31, 2010 performance period	Dec. 31, 2011 Three-Year Performance RSUs January 1, 2008 to December 31, 2010 performance period	Dec. 31, 2009 Three-Year Performance RSUs January 1, 2009 to December 31, 2011 performance period	Dec. 31, 2011 Three-Year Performance RSUs January 1, 2009 to December 31, 2011 performance period	Dec. 31, 2010 Three-Year Performance RSUs January 1, 2010 to December 31, 2012 performance period	Dec. 31, 2011 Three-Year Performance RSUs January 1, 2010 to December 31, 2012 performance period	Dec. 31, 2011 Three-Year Performance RSUs January 1, 2011 to December 31, 2013 performance period	Dec. 31, 2011 Stock Options Y	Dec. 31, 2010 Stock Options	Dec. 31, 2009 Stock Options	Dec. 31, 2011 Service RSUs Y	Dec. 31, 2010 Service RSUs	Dec. 31, 2009 Service RSUs	Dec. 31, 2011 Performance RSUs Y	Dec. 31, 2010 Performance RSUs	Dec. 31, 2011 2009 Plan	Dec. 31, 2011 2009 Plan Stock Options	Dec. 31, 2011 2009 Plan Performance RSUs	Dec. 31, 2011 Non-Employee Directors Plan	Dec. 31, 2011 Partners Plan Two-Year Performance RSUs Y	Dec. 31, 2011 Partners Plan Three-Year Performance RSUs	Dec. 31, 2011 Senior Partners Plan Three-Year Performance RSUs
Stock-Based Compensation Plans
Maximum number of shares available for grant																																		2,600,000	1,000,000		100,000
Maximum number of awards that can be awarded in a three year period to an individual (in shares)																																		1,000,000
Maximum dollar amount available for grant to an individual per calendar year																																				$ 5,000,000
Common stock available for issuance																																		798,954			44,933
Number of stock-based compensation plans with outstanding awards	6
Expenses relating to stock-based compensation arrangements	28,100,000	35,300,000	13,200,000
Income tax benefits recognized related to stock-based compensation arrangements	9,700,000	12,300,000	4,500,000
Net cash received (paid) from exercise of stock-based compensation	(5,700,000)		1,600,000
Cash savings resulting from excess tax benefits		300,000	200,000
Income tax benefits realized on stock-based compensation exercises	6,400,000	2,600,000	800,000
Vesting rights																										25% on each anniversary date of the grant for four years			The great majority will vest on the the third anniversary of the date of grant
Minimum vesting period from the date of grant (in years)																													P1Y
Maximum vesting period from the date of grant (in years)																										P4Y			P4Y
Tenure of awards (in years)																										P10Y
Stock option, Number of shares
Outstanding at the beginning of the period (in shares)																										2,024,855
Exercised (in shares)																										(1,875)
Forfeited or expired (in shares)																										(232,933)
Outstanding at the end of the period (in shares)																										1,790,047	2,024,855
Exercisable at the end of the period (in shares)																										1,740,672
Stock options, Weighted average exercise price
Outstanding at the beginning of the period (in dollars per share)																										$ 63.00
Exercised (in dollars per share)																										$ 52.68
Forfeited or expired (in dollars per share)																										$ 72.52
Outstanding at the end of the period (in dollars per share)																										$ 61.77	$ 63.00
Exercisable at the end of the period (in dollars per share)																										$ 61.57
Stock options, Weighted average remaining contractual life
Outstanding at the end of the period (in years)																										3.0
Exercisable at the end of the period (in years)																										2.9
Stock options, Aggregate intrinsic value
Outstanding at the end of the period (in dollars)																										503,000
Exercisable at the end of the period (in dollars)																										503,000
Aggregate intrinsic value of options exercised																											200,000	1,600,000
Number of options that vested during the period (in shares)																										102,000	102,000	167,000
Aggregate grant-date fair values of options vested																										2,200,000	2,200,000	3,600,000
Unrecognized stock-based compensation expense
Unrecognized stock-based compensation expense related to non-vested awards																										100,000			8,400,000			11,200,000
Weighted-average period of recognition of unrecognized stock-based compensation expenses of non-vested awards (in years)																										0.1			1.4			1.6
Unvested restricted stock units, number of shares
Outstanding at the beginning of the period (in shares)																													794,396			1,009,360
Granted (in shares)				42,925		87,683		92,925		201,200		220,850			12,000		27,000		31,500		63,300		69,000		185,975				105,028	311,640	411,390	185,975
Additional RSUs resulting from satisfaction of performance condition (in shares)																																24,760
Vested (in shares)																													(215,654)	(112,859)	(21,552)	(158,216)	(42,960)
Forfeited or expired (in shares)																													(5,900)			(477)
Outstanding at the end of the period (in shares)																													677,870	794,396		1,061,402	1,009,360
Unvested restricted stock units, weighted average grant date value
Outstanding at the beginning of the period (in dollars per share)																													$ 46.42			$ 49.14
Granted (in dollars per share)																													$ 43.93			$ 43.89
Additional RSUs resulting from satisfaction of performance (in dollars per share)																																$ 31.91
Vested (in dollars per share)																													$ 56.40			$ 63.14
Forfeited or expired (in dollars per share)																													$ 44.17			$ 65.98
Outstanding at the end of the period (in dollars per share)																													$ 42.89	$ 46.42		$ 45.74	$ 49.14
Additional disclosure of non-vested restricted stock units
Weighted average remaining contractual life (in years)																													0.8			1.0
Aggregate intrinsic value of restricted stock units (in thousands)																													$ 37,100,000			$ 58,091,000
Additional disclosure of performance based RSUs
Requisite performance period														3																								2
Shares issued per RSU (in shares)														1																								1
Percentage of awarded number of performance RSU based on BVPS growth target, minimum																																						25.00%	25.00%	25.00%
Percentage of awarded number of performance RSU based on BVPS growth target, maximum																																						150.00%	150.00%	200.00%
Minimum percentage of growth target to earn performance RSU																																						25.00%	25.00%	50.00%
Performance RSUs Granted (in shares)				42,925		87,683		92,925		201,200		220,850			12,000		27,000		31,500		63,300		69,000		185,975				105,028	311,640	411,390	185,975
Maximum number of performance RSUs available to be earned (in shares)					64,387		131,525		139,388		301,800		331,275			24,000		54,000		63,000		126,600		138,000	278,939
Actual performance RSUs earned (in shares)					64,387		100,913		120,374		296,925		205,698			21,552		48,090		50,866		103,212

TRANSATLANTIC HOLDINGS INC 10-K