Income Taxes - Uncertain Income Tax Positions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Uncertain income tax positions [Roll Forward]
Uncertain income tax positions, beginning balance	$ 993	$ 950
Increases in balances related to tax positions taken during current period	91	43
Uncertain income tax positions, ending balance	$ 1,084	$ 993