Fair value of financial instruments - Differences Between Fair Value and Principal Balance for Loans Held for Sale Measured at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale measured at fair value	$ 672,924	$ 683,770
Nonaccrual loans	5,217	6,406
Fair Value | Past due 90 days or more
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale measured at fair value		83
Fair Value | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale measured at fair value	74,082	208,914
Aggregate Unpaid Principal Balance
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale measured at fair value	658,017	651,887
Nonaccrual loans	9,899	12,033
Aggregate Unpaid Principal Balance | Past due 90 days or more
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale measured at fair value		163
Aggregate Unpaid Principal Balance | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale measured at fair value	76,863	226,867
Difference
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale measured at fair value	14,907	31,883
Nonaccrual loans	(4,682)	(5,627)
Difference | Past due 90 days or more
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale measured at fair value		(80)
Difference | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale measured at fair value	$ (2,781)	$ (17,953)