Bank segment - Contractual maturities of investment securities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Available-for-sale
Due in one year or less	$ 15,807		$ 15,807
Due after one year through five years	84,406		84,406
Due after five years through ten years	66,788		66,788
Due after ten years	0		0
Total amortized cost	167,001		167,001
Mortgage-backed securities — issued or guaranteed by U.S. Government agencies or sponsored agencies	2,606,904		2,606,904
Amortized cost	2,773,905		2,773,905
Held-to-maturity
Due in one year or less	0		0
Due after one year through five years	0		0
Due after five years through ten years	59,882		59,882
Due after ten years	0		0
Total amortized cost	59,882		59,882
Mortgage-backed securities — issued or guaranteed by U.S. Government agencies or sponsored agencies	453,885		453,885
Amortized cost	513,767		513,767
Available-for-sale
Due in one year or less	15,781		15,781
Due after one year through five years	81,286		81,286
Due after five years through ten years	62,014		62,014
Due after ten years	0		0
Total fair value	159,081		159,081
Mortgage-backed securities — issued or guaranteed by U.S. Government agencies or sponsored agencies	2,285,186		2,285,186
Total available-for-sale securities	2,444,267		2,444,267		$ 2,574,618
Held-to-maturity
Due in one year or less	0		0
Due after one year through five years	0		0
Due after five years through ten years	53,885		53,885
Due after ten years	0		0
Total fair value	53,885		53,885
Mortgage-backed securities — issued or guaranteed by U.S. Government agencies or sponsored agencies	386,138		386,138
Total held-to-maturity securities	440,023		440,023
Proceeds, gross gains and losses from sales of available-for-sale securities
Proceeds	0	$ 0	0	$ 197,354
Gross gains	0	0	0	975
Gross losses	0	0	0	447
Tax expense on realized gains	$ 0	$ 0	$ 0	$ 142