Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenue from Contracts with Customers
Revenue	$ 255,646	$ 291,724	$ 344,065
Contra revenue charge	83,641	0	0
Volume -Related
Revenue from Contracts with Customers
Revenue	218,540	245,300	273,535
Gain (Loss) changes in fair value	(3,500)	2,100	(6,600)
Station construction sales
Revenue from Contracts with Customers
Revenue	16,406	26,593	23,120
AFTC
Revenue from Contracts with Customers
Revenue	$ 20,700	$ 19,831	47,123
Other
Revenue from Contracts with Customers
Revenue			$ 287