Bank segment - Collateral-dependent loans (Details) $ in Thousands	Mar. 31, 2020 USD ($)
Financing Receivable, Nonaccrual [Line Items]
Collateral-dependent loans, amortized cost	$ 5,180,378
Residential 1-4 family
Financing Receivable, Nonaccrual [Line Items]
Collateral-dependent loans, amortized cost	2,161,894
Residential 1-4 family | Residential real estate property
Financing Receivable, Nonaccrual [Line Items]
Collateral-dependent loans, amortized cost	2,315
Home equity line of credit
Financing Receivable, Nonaccrual [Line Items]
Collateral-dependent loans, amortized cost	1,095,677
Home equity line of credit | Residential real estate property
Financing Receivable, Nonaccrual [Line Items]
Collateral-dependent loans, amortized cost	1,567
Commercial real estate
Financing Receivable, Nonaccrual [Line Items]
Collateral-dependent loans, amortized cost	852,120
Commercial real estate | Commercial real estate property
Financing Receivable, Nonaccrual [Line Items]
Collateral-dependent loans, amortized cost	2,290
Total real estate
Financing Receivable, Nonaccrual [Line Items]
Collateral-dependent loans, amortized cost	6,172
Commercial loans
Financing Receivable, Nonaccrual [Line Items]
Collateral-dependent loans, amortized cost	722,647
Commercial loans | Business assets
Financing Receivable, Nonaccrual [Line Items]
Collateral-dependent loans, amortized cost	90
Collateral Pledged
Financing Receivable, Nonaccrual [Line Items]
Collateral-dependent loans, amortized cost	$ 6,262