Income Taxes - Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Beginning balance	$ 20,483	$ 18,413	$ 17,384
Reductions	0	0	0
Reductions	0	(802)	0
Settlements	0	0	0
Lapses in statute of limitations	0	0	0
Ending balance	27,419	20,483	18,413
Federal [Member]
Income Tax Contingency [Line Items]
Tax positions related to current year, Additions	2,019	1,206	530
Tax positions related to prior year, Additions	669	0	0
State [Member]
Income Tax Contingency [Line Items]
Tax positions related to current year, Additions	3,645	1,666	499
Tax positions related to prior year, Additions	603	0	0
Foreign [Member]
Income Tax Contingency [Line Items]
Tax positions related to prior year, Additions	$ 0	$ 0	$ 0