Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Effective Federal Statutory Income Tax Rate, Percent	31.10%	26.20%	31.30%
Liability for unrecognized tax benefits	$ 40,376			$ 40,376	$ 32,776
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	37,533			37,533
Increase in liability for unrecognized tax benefits				7,600
Accrued interest and penalties related to unrecognized tax benefits, net of federal tax benefits	$ 8,296			$ 8,296	$ 4,195