Credit Facility - Interest expense and unused line of credit fees (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Credit Facility
Interest expense	$ 703		$ 703
Amortization of debt issuance costs	45		45
Unused line of credit fees	60	$ 57	179	$ 171
Total interest expense	$ 808	$ 57	$ 927	$ 171