Assets Manufactured for Internal Use, net - Components (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets manufactured for internal use
Cost	$ 48,352	$ 40,709
Accumulated depreciation	(18,512)	(15,381)
Net	29,840	25,328
Depreciation expense	$ 3,400	2,600	$ 3,200
Assets Manufactured for Internal Use
Assets manufactured for internal use
Useful life	10 years
Cost	$ 62,618	62,017
Accumulated depreciation	(24,155)	(19,259)
Net	38,463	42,758
Depreciation expense	5,200	3,900	$ 2,600
Assets Manufactured for Internal Use | Internal use assets
Assets manufactured for internal use
Cost	62,462	56,775
Assets Manufactured for Internal Use | Construction in process.
Assets manufactured for internal use
Cost	$ 156	$ 5,242