Commitments and contingencies Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Commitments to Extend Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability	$ 3,561,078	$ 3,301,692
Standby Letters of Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability	20,385	20,686
Deferred standby letter of credit fees [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability	169	164
Obligation to Repurchase Receivables Sold [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability	$ 261,713	$ 303,265