Income Taxes - Schedule of Additional Information Relating to Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Unrecognized tax benefits at the end of the year that, if recognized, would favorably affect the effective tax rate (includes interest and penalties of $15,136, $15,392 and $13,083, respectively)	$ 78,841	$ 81,564	$ 74,785
Unrecognized tax benefits that, if recognized, would not affect the effective tax rate	14,969	12,224	15,578
Interest and penalties recognized in current income tax expense (after giving effect to the reversal of interest and penalties of $6,185, $3,143 and $3,865, respectively)	$ (256)	$ 2,309	$ 79