Income Taxes - Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Unrecognized Income Tax Benefit [Roll Forward]
Beginning balance, unrecognized tax benefits	$ 31,558	$ 26,155	$ 21,834
Additions based on tax provisions related to the current year	3,755	4,143	3,332
Additions for tax positions due to acquisitions		9,208
Additions based on tax provisions related to the prior year	3,000	1,171	2,496
Deductions based on settlement/expiration of prior year tax positions	(4,161)	(9,119)	(1,507)
Ending balance, unrecognized tax benefits	$ 34,152	$ 31,558	$ 26,155