Bank segment - Contractual maturities of investment securities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Available-for-sale
Due in one year or less	$ 15,239		$ 15,239
Due after one year through five years	81,842		81,842
Due after five years through ten years	66,642		66,642
Due after ten years	0		0
Total amortized cost	163,723		163,723
Mortgage-backed securities — issued or guaranteed by U.S. Government agencies or sponsored agencies	2,533,445		2,533,445
Amortized cost	2,697,168		2,697,168
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	59,888		59,888
Due after ten years	0		0
Total amortized cost	59,888		59,888
Mortgage-backed securities — issued or guaranteed by U.S. Government agencies or sponsored agencies	450,991		450,991
Amortized cost	510,879		510,879
Available-for-sale
Due in one year or less	15,195		15,195
Due after one year through five years	76,442		76,442
Due after five years through ten years	59,744		59,744
Due after ten years	0		0
Total fair value	151,381		151,381
Mortgage-backed securities — issued or guaranteed by U.S. Government agencies or sponsored agencies	2,080,955		2,080,955
Total available-for-sale securities	2,232,336		2,232,336		$ 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	50,970		50,970
Due after ten years	0		0
Total fair value	50,970		50,970
Mortgage-backed securities — issued or guaranteed by U.S. Government agencies or sponsored agencies	360,221		360,221
Total held-to-maturity securities	411,191		411,191
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