Commitments and Contingencies - Components of lease expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating lease costs:
Operating lease rental expense	$ 328
Sublease income	(299)
Total operating lease costs	29
Finance lease costs:
Amortization of right-of-use assets	2
Total finance lease costs	$ 2
Operating lease costs:
Operating lease rental expense		$ 306
Sublease income		(328)
Total operating lease costs		(22)
Finance lease costs:
Amortization of right-of-use assets		3
Interest on lease liabilities		1
Total finance lease costs		$ 4