Credit Facility - Interest expense and unused line of credit fees (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Credit Facility
Interest expense	$ 2,994
Amortization of debt issuance costs	186
Unused line of credit fees	236	$ 228	$ 66
Total interest expense	$ 3,416	$ 228	$ 66