Notes Payable (Details) - USD ($) $ in Thousands	1 Months Ended	7 Months Ended	12 Months Ended
	Jul. 31, 2017	Jul. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Notes Payable
Proceeds from the issuance of debt					$ 28,278
Interest Expense			$ 159	$ 464	475
Credit facility
Notes Payable
Proceeds from the issuance of debt						$ 7,000
Term loans balance paid in full	$ 3,500
Penalty for prepayment	$ 0
Accrued interest rate (as a percent)	6.50%	6.50%
Monthly payments (as a percent)		4.17%
Interest Expense			200	$ 500	$ 500
Accrued interest			$ 0
Credit facility | Prime rate
Notes Payable
Variable interest rate		prime rate
Variable rate basis (as a percent)		3.25%