Income Taxes - Reconciliation of Total Amounts of Gross Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 2,886	$ 731	$ 814
Gross increases—tax positions in prior years	3,259	1,503	92
Gross decreases—tax positions in prior years	(8)	(257)	0
Gross increases—tax positions in current year	2,284	956	114
Settlements	0	(40)	0
Lapse of statute of limitations	(3)	(7)	(289)
Balance at end of period	$ 8,418	$ 2,886	$ 731