Income taxes - Allocation of Federal and State Income Taxes between Current and Deferred Portions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Current	$ 21,980	$ 44,362	$ 27,641
Deferred	30,770	(25,530)	(1,916)
Total	$ 52,750	$ 18,832	$ 25,725