Income taxes - Reconciliation of Income Tax Expenses Computed at Federal Statutory Rate with Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Effective Tax Rate Reconciliation [Line Items]
Expected income tax expense at 21%	$ 87,613	$ 42,785	$ 22,116
State income tax expense - net of Federal impact	8,201	2,944	818
Valuation allowance	(4,427)	2,427	1,326
Nondeductible expenses	4,090	2,399	3,249
Research and development credits	(398)	(1,055)	(278)
Return-to-provision and true-up adjustments	(1,617)	(438)	(776)
Other – net	(892)	(216)	(511)
Total income tax expense	$ 93,989	$ 48,833	$ 26,695
Effective income tax rate	22.50%	24.00%	25.30%
Foreign
Effective Tax Rate Reconciliation [Line Items]
Foreign income tax rate differential	$ 3,549	$ 1,465	$ 138
Canada
Effective Tax Rate Reconciliation [Line Items]
Foreign income tax rate differential	$ (2,130)	$ (1,478)	$ 613