Stock incentive plan - Non vested restricted stock award (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance	6,573
Ending Balance	5,793	6,573
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance	25,247
Shares, Granted	6,724
Shares, Vested	(8,838)
Shares, Forfeited	0	(1,094)
Shares, Other	(601)
Ending Balance	23,734	25,247
Weighted-Average Grant-Date Fair-Value, Beginning Balance	$ 30.88
Weighted-Average Grant-Date Fair-Value, Granted	54.48
Weighted-Average Grant-Date Fair-Value, Vested	31.26
Weighted-Average Grant Date Fair Value, Other	31.86
Weighted-Average Grant-Date Fair-Value, Ending Balance	$ 37.45	$ 30.88
Aggregate Intrinsic Value, Beginning Balance	$ 1,460,539
Aggregate Intrinsic Value, Vested	(511,278)
Aggregate Intrinsic Value, Other	(34,768)
Aggregate Intrinsic Value, Ending Balance	$ 1,373,012	$ 1,460,539