Income Taxes - Reconciliation of Differences between Income Tax Provision and Income Tax Determined by Applying US Federal Statutory Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount [Abstract]
U.S. Federal statutory taxes	$ 49,671	$ 35,990	$ 26,876
State and local taxes, net of U.S. Federal benefit	5,110	3,747	2,806
Permanent items	576	396	1,308
Excess tax benefits from vesting or settlement of stock compensation awards	(1,454)	(1,749)
Domestic production activities deduction	(4,376)	(2,740)	(2,262)
Federal credits	(534)	(488)	(328)
Other	(2,202)	(173)	289
Total income tax provision	$ 46,791	$ 34,983	$ 28,689