Income Taxes - Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Income Taxes
Statutory Federal income tax rate (as a percent)	21.00%	35.00%
Net deferred tax assets
Net deferred tax assets	$ 27,928	$ 16,247
Valuation allowance for deferred tax assets	$ 0