Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]
Income tax expense (benefit)	$ 26	$ 122	$ 111	$ 276
Effective income tax rate	(0.10%)	(0.70%)	(0.30%)	(0.70%)