Income Taxes - Schedule of Effective Income Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Computed “expected” tax provision (benefit)	$ 90,700	$ 11,700	$ 14,700
Change in income tax resulting from:
State taxes, net of federal benefit	8,500	1,400	2,500
Change in federal tax rate	(17,300)
Other	900		(800)
Total provision (benefit) for taxes	$ 82,809	$ 13,121	$ 16,414