Commitments and contingencies - Financial Instruments with Off-Balance Sheet Credit Risk (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Balance at end of period	$ 3,184,021	$ 2,787,594
Commitments to extend credit, excluding interest rate lock commitments
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Balance at end of period	3,106,594	2,719,996
Letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Balance at end of period	$ 77,427	$ 67,598