Income tax expense (benefit) (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Current:
Federal	$ 17,121	$ 65,006	$ (3,502)
State	11,549	21,234	3,366
Foreign	0	151	0
Current income taxes	28,670	86,391	(136)
Deferred:
Federal	45,885	(3,735)	50,218
State	12,610	(625)	12,098
Investment tax credit - net	1,755	2,559	1,099
Deferred income taxes	60,250	(1,801)	63,415
Total income tax expense	$ 88,920	$ 84,590	$ 63,279