Income Taxes - Schedule of Unrecognized Tax Benefits Roll Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Abstract]
Unrecognized tax benefits, opening balance	$ 4,827	$ 5,236	$ 5,292
Gross increases—tax positions in prior period	171	118	136
Gross decreases—tax positions in prior period	(362)	(735)	(755)
Gross increases—current-period tax positions	244	208	563
Lapse of statute of limitations	0	0	0
Unrecognized tax benefits, ending balance	$ 4,880	$ 4,827	$ 5,236