Income Taxes - Reconciliation of Total Amounts of Gross Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 731	$ 814	$ 4,573
Gross increases—tax positions in prior years	1,503	92	0
Gross decreases—tax positions in prior years	(257)	0	(1,807)
Gross increases—tax positions in current year	956	114	120
Settlements	(40)	0	(520)
Lapse of statute of limitations	(7)	(289)	(1,552)
Balance at end of period	$ 2,886	$ 731	$ 814