Income Taxes - Reconciliation of Beginning and Ending Amount of Gross Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at January 1,	$ 45,146	$ 56,721
Increase based upon tax positions of current year	0	1,183
Increase (decrease) based upon tax positions of a prior year	1,022
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions		(6,839)
Unrecognized tax benefits, decrease due to changes in tax rates	0	(3,408)
Decrease based upon settlements with taxing authorities	(1,253)	(2,191)
Decrease based upon a lapse in the statute of limitations	(1,407)	(320)
Balance at December 31,	$ 43,508	$ 45,146