Fair value of financial instruments - Loans Held for Sale at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total loans held for sale	$ 752,223	$ 899,173
Commercial and industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total loans held for sale	79,299	215,403
Residential real estate | 1-to-4 family mortgage
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total loans held for sale	672,924	683,770
Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total loans held for sale	752,223	899,173
Recurring Basis | Commercial and industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total loans held for sale	79,299	215,403
Recurring Basis | Residential real estate | 1-to-4 family mortgage
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total loans held for sale	$ 672,924	$ 683,770