Income Taxes - Reconciliation of Differences between Income Tax Provision (Benefit) and Income Tax Determined by Applying US Federal Statutory Rate (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Effective Income Tax Rate Reconciliation, Amount [Abstract]
U.S. federal statutory taxes	$ 23,432	$ 8,417	$ 1,305
State and local taxes, net of U.S. federal benefit	2,856	1,061	(418)
Permanent items	(868)	225	198
Federal credits	(214)	(566)	(54)
Other	(43)	244	46
Increase (decrease) in valuation allowance	264	(19,930)	(68)
Total income tax provision (benefit)	$ 25,427	$ (10,549)	$ 1,009