Income Tax - Reconciliation of U.S. Statutory Income Tax Rate to Effective Income Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal income tax expense at statutory rate	$ 33,566	$ 32,733	$ 57,209
State income tax, net of federal income tax benefit	6,999	7,953	4,754
Domestic production activities deduction	0	0	(2,617)
Excess tax benefits related to stock option exercises	(29,819)	(32,487)	(40,624)
Tax Act adjustments	0	(1,750)	(25,992)
Tax credits	(3,446)	(3,715)	(3,578)
Non-deductible business expenses	6,011	5,655	4,573
Other, net	0	19	160
Income tax expense benefit	$ 13,311	$ 8,408	$ (6,115)