Select balance sheet data - Schedule of Changes In Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Select Balance Sheet Data [Abstract]
Balance				$ 72,173					$ 72,173
Amortization expense	$ (2,676)	$ (2,677)	$ (2,677)	$ (2,677)	$ (2,677)	$ (2,677)	$ (2,677)	$ (2,677)	(10,706)	$ (10,706)	$ (4,096)
Balance	$ 61,467				$ 72,173				$ 61,467	$ 72,173