Income Taxes - Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 77,410	$ 27,419	$ 20,483
Tax positions related to current year, Additions	2,512	49,858	5,664
Reductions	0	0	0
Tax positions related to prior year, Additions	193	277	1,272
Reductions	(1,450)	(144)	0
Settlements	0	0	0
Lapses in statute of limitations	0	0	0
Ending balance	$ 78,665	$ 77,410	$ 27,419