Commitments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating leases
Rent expense			$ 1,100	$ 1,300
Future minimum payments required under the non-cancelable operating lease
2019				1,421
2020				721
Total minimum lease payments				$ 2,142
Amount of base rent from sub-lease	$ 500	$ 1,100
Sublease income			$ 300