Accounts Payable and Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts Payable and Accrued Liabilities
Accounts payable	$ 7,401	$ 4,517
Accrued expenses	2,453	2,004
Accrued compensation	5,253	6,477
Accounts Payable and Accrued Expenses	$ 15,107	$ 12,998