Income Taxes - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Beginning balance	$ 2,471	$ 1,474	$ 719
Increases (decreases) of unrecognized tax benefits related to prior year	289	(97)
Increases of unrecognized tax benefits related to current year	1,050	1,094	755
Ending balance	$ 3,810	$ 2,471	$ 1,474