Investment Securities (Summary of Held-to-Maturity Debt Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Schedule of Investments [Line Items]
Amortized Cost	$ 6,362,458	$ 6,198,339
Unrealized Gains	20,799	138,254
Unrealized Losses	(291,640)	(55,657)
Fair Value	6,091,617	6,280,936
Allowance	204	214	$ 308	$ 299
Net Carrying Value	6,362,254	6,198,125
Interest receivable	17,300	21,200
Agency CMO
Schedule of Investments [Line Items]
Amortized Cost	36,533	42,405
Unrealized Gains	54	655
Unrealized Losses	(856)	(25)
Fair Value	35,731	43,035
Allowance	0	0
Net Carrying Value	36,533	42,405
Agency MBS
Schedule of Investments [Line Items]
Amortized Cost	2,915,114	2,901,593
Unrealized Gains	8,452	71,444
Unrealized Losses	(128,688)	(11,788)
Fair Value	2,794,878	2,961,249
Allowance	0	0
Net Carrying Value	2,915,114	2,901,593
Agency CMBS
Schedule of Investments [Line Items]
Amortized Cost	2,548,347	2,378,475
Unrealized Gains	33	11,202
Unrealized Losses	(153,778)	(43,844)
Fair Value	2,394,602	2,345,833
Allowance	0	0
Net Carrying Value	2,548,347	2,378,475
Municipal bonds and notes
Schedule of Investments [Line Items]
Amortized Cost	696,601	705,918
Unrealized Gains	12,198	51,572
Unrealized Losses	(4,138)	0
Fair Value	704,661	757,490
Allowance	204	214
Net Carrying Value	696,397	705,704
CMBS
Schedule of Investments [Line Items]
Amortized Cost	165,863	169,948
Unrealized Gains	62	3,381
Unrealized Losses	(4,180)	0
Fair Value	161,745	173,329
Allowance	0	0
Net Carrying Value	$ 165,863	$ 169,948

Amount, after allowance for credit loss, of accrued interest on investment in debt security measured at amortized cost (held-to-maturity).

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