Property and Equipment - Depreciation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Property and equipment
Depreciation and amortization expense	$ 2,099	$ 540	$ 4,083	$ 1,404