Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]
Income tax expense (benefit)	$ 166	$ 62	$ 277	$ 338
Effective income tax rate	(1.70%)	(0.40%)	(0.50%)	(0.70%)