Employee Benefit Plans - Projected Benefit Obligation (Details) - USD ($) $ in Thousands	3 Months Ended						12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in projected benefit obligation:
Settlement loss	$ 600	$ 1,100	$ 300	$ 2,000	$ 800	$ 500
Change in plan assets:
Fair value of plan assets at beginning of period				167,843			$ 167,843
Fair value of plan assets at end of period	166,587				167,843		166,587	$ 167,843
Amounts recognized on balance sheet:
Other current liabilities	(3,226)				(3,332)		(3,226)	(3,332)
Employee benefit obligation, noncurrent	(79,953)				(105,930)		(79,953)	(105,930)
Pension
Change in projected benefit obligation:
Obligation at beginning of period				203,316			203,316	203,455
Interest cost							6,705	7,347
Settlement loss							3,995	1,277	$ 8,088
Actuarial (gain) loss							11,574	3,686
Benefits paid							(26,962)	(11,172)
Projected benefit obligation at end of period	194,633				203,316		194,633	203,316	203,455
Change in plan assets:
Fair value of plan assets at beginning of period				167,843			167,843	156,678
Return on plan assets							22,525	13,032
Employer contributions							3,181	9,305
Benefits paid							(26,962)	(11,172)
Fair value of plan assets at end of period	166,587				167,843		166,587	167,843	156,678
Funded status:
Plan assets less than projected benefit obligation	(28,046)				(35,473)		(28,046)	(35,473)
Amounts recognized on balance sheet:
Employee benefit obligation, noncurrent	(28,046)				(35,473)		(28,046)	(35,473)
Net amount recognized	(28,046)				(35,473)		(28,046)	(35,473)
Actuarial loss recognized in accumulated other comprehensive income (loss)	(31,886)				$ (36,919)		(31,886)	(36,919)
Actuarial assumptions:
Benefits obligation settlement							23,000	$ 7,100	55,900
Other comprehensive gain (loss) due to the results of fair value of plan assets							19,700
Estimated future amount of loss to be amortized from accumulated other comprehensive income (loss)	$ 400						$ 400
Pension \| Minimum
Actuarial assumptions:
Discount rate used to measure the plan obligations (as percent)	3.50%				3.81%		3.50%	3.81%
Pension \| Maximum
Actuarial assumptions:
Discount rate used to measure the plan obligations (as percent)	3.50%				3.85%		3.50%	3.85%
Other Postretirement Benefits
Change in projected benefit obligation:
Obligation at beginning of period				$ 73,789			$ 73,789	$ 60,749
Service cost							898	1,104	1,088
Interest cost							2,193	2,637
Actuarial (gain) loss							(1,641)	11,036
Plan change							(18,262)
Benefits paid							(1,844)	(1,737)
Projected benefit obligation at end of period	$ 55,133				$ 73,789		55,133	73,789	$ 60,749
Change in plan assets:
Employer contributions							1,844	1,737
Benefits paid							(1,844)	(1,737)
Funded status:
Plan assets less than projected benefit obligation	(55,133)				(73,789)		(55,133)	(73,789)
Amounts recognized on balance sheet:
Other current liabilities	(3,226)				(3,332)		(3,226)	(3,332)
Employee benefit obligation, noncurrent	(51,907)				(70,457)		(51,907)	(70,457)
Net amount recognized	(55,133)				(73,789)		(55,133)	(73,789)
Actuarial loss recognized in accumulated other comprehensive income (loss)	$ (816)				$ (20,040)		$ (816)	$ (20,040)
Actuarial assumptions:
Assumed health care cost trend rate, current (as a percent)	7.25%				7.50%		7.25%	7.50%	6.75%
Assumed health care cost trend rate, current (as a percent)							7.00%	7.25%
Assumed health care cost trend rate, ultimate (as a percent)	5.00%				5.00%		5.00%	5.00%	5.00%
Assumed health care cost trend rate, ultimate (as a percent)							5.00%	5.00%
Estimated future amount of loss to be amortized from accumulated other comprehensive income (loss)	$ 900						$ 900
Other Postretirement Benefits \| Minimum
Actuarial assumptions:
Discount rate used to measure the plan obligations (as percent)	3.62%				4.03%		3.62%	4.03%
Other Postretirement Benefits \| Maximum
Actuarial assumptions:
Discount rate used to measure the plan obligations (as percent)	3.63%				4.25%		3.63%	4.25%

Hawaiian Telcom Holdco, Inc. 10-K