Provision for 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
Reconciliation Of Unrecognized Tax Benefits Excluding Amounts Pertaining To Examined Tax Returns Roll Forward
Beginning balance	$ 622	$ 242	$ 19
Additions for tax positions taken in a prior year	8	29
Additions for tax positions taken in current year	454	351	223
Ending balance	$ 1,084	$ 622	$ 242