Fair Value - Assets and Liabilities Measured at Fair Value on Recurring and Nonrecurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in debt securities, available-for-sale	$ 151,426	$ 119,307
Loans	2,633,032	2,838,165
Loans held-for-sale	354,242	145,406
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	145,676	69,875
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	2,633,032	2,838,165
Loans held-for-sale	208,566	75,531
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in debt securities, available-for-sale	151,426	119,307
Loans	403,129	403,745
Total assets recorded at fair value on a recurring basis	554,555	523,052
Contingent consideration liability		1,350
Total liabilities recorded at fair value on a recurring basis		1,350
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	403,129	403,745
Total assets recorded at fair value on a recurring basis	403,129	403,745
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in debt securities, available-for-sale	151,426	119,307
Total assets recorded at fair value on a recurring basis	151,426	119,307
Contingent consideration liability		1,350
Total liabilities recorded at fair value on a recurring basis		1,350
Nonrecurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	33,107	6,924
Other real estate owned/repossessed assets	15,632	15,750
Total assets recorded at fair value on a nonrecurring basis	48,739	22,674
Nonrecurring Basis [Member] \| Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	26,032	4,465
Total assets recorded at fair value on a nonrecurring basis	26,032	4,465
Nonrecurring Basis [Member] \| Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	7,075	2,459
Other real estate owned/repossessed assets	15,632	15,750
Total assets recorded at fair value on a nonrecurring basis	$ 22,707	$ 18,209

NewStar Financial, Inc. 10-Q