Investment (Held-to-Maturity) Securities (Details) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2024 USD ($)		Dec. 31, 2023 USD ($)
Schedule of Investment (Held-to-Maturity) Securities [Line Items]
Investment Securities, Gross Amortized Cost		$ 2,338,460		$ 2,409,090
Investment Securities, Gross Carrying Value		2,186,043	[1]	2,244,489	[2]
Investment securities, Allowance for Credit Loss		(299)	[1]	(336)	[2]
Investment Securities, Amortized Cost, After Allowance for Credit Loss		2,338,161		2,408,754
Investment Securities, Carrying Value, after Allowance for Credit Loss		2,185,744	[1]	2,244,153	[2]
Investment Securities, Fair Value		2,000,065		2,072,586
Investment Securities, Gross Unrealized Gain		3,927		5,139
Investment Securities, Gross Unrealized Loss		(189,905)		(177,042)
Debt Securities, Net Unrealized Loss Remaining in AOCI included in Carrying Value for AFS Securities Transferred to Investment Securities		$ (152,000)		$ (165,000)
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		141		134
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 17,310		$ 1,931
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		1,887,274		1,947,071
Investment Securities, Continuous Unrealized Loss Position, Fair Value		1,904,584		1,949,002
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		81		5
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		189,824		177,037
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss		189,905		177,042
Fixed Maturity Securities [Member]
Investment Securities, Debt Maturities, Net Carrying Value [Abstract]
Investment Securities, Debt Maturities, Less than One Year, Net Carrying Value		19,248
Investment Securities, Debt Maturities, One to Five Years, Net Carrying Value		95,707
Investment Securities, Debt Maturities, Six to Ten Years, Net Carrying Value		26,103
Investment Securities, Debt Maturities, Over Ten Years, Net Carrying Value		13
Investment Securities, Debt Maturities, Single Maturity Date, Net Carrying Value		141,071
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Investment Securities, Debt Maturities, Less Than One Year, Fair Value		19,468
Investment Securities, Debt Maturities, One to Five Years, Fair Value		98,033
Investment Securities, Debt Maturities, Six to Ten Years, Fair Value		24,524
Investment Securities, Debt Maturities, Over Ten Years, Fair Value		13
Investment Securities, Debt Maturities, Single Maturity Date, Fair Value		$ 142,038
Investment Securities, Debt Maturities, Weighted Average Maturity	[3]	3.27
Municipal securities [Member]
Schedule of Investment (Held-to-Maturity) Securities [Line Items]
Investment Securities, Gross Amortized Cost		$ 108,793		120,705
Investment Securities, Gross Carrying Value		108,793	[1]	120,705	[2]
Investment Securities, Fair Value		112,338		125,525
Investment Securities, Gross Unrealized Gain		3,828		5,014
Investment Securities, Gross Unrealized Loss		$ (283)		$ (194)
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		20		13
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 17,310		$ 1,931
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		6,587		6,600
Investment Securities, Continuous Unrealized Loss Position, Fair Value		23,897		8,531
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		81		5
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		202		189
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss		283		194
Residential agency mortgage-backed securities [Member]
Schedule of Investment (Held-to-Maturity) Securities [Line Items]
Investment Securities, Gross Amortized Cost		2,196,121		2,255,340
Investment Securities, Gross Carrying Value		2,044,972	[1]	2,092,083	[2]
Investment Securities, Fair Value		1,858,027		1,917,810
Investment Securities, Gross Unrealized Gain		99		125
Investment Securities, Gross Unrealized Loss		(187,044)		$ (174,398)
Investment Securities, Debt Maturities, Net Carrying Value [Abstract]
Investment Securities, Debt Maturities, without Single Maturity Date, Net Carrying Value	[4]	2,044,972
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Investment Securities, Debt Maturities, without Single Maturity Date, Fair Value		$ 1,858,027
Investment Securities, Debt Maturities, Average Expected Life of Mortgage-backed Securities		4 years 10 months 24 days
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		116		116
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 0		$ 0
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		1,857,000		1,916,732
Investment Securities, Continuous Unrealized Loss Position, Fair Value		1,857,000		1,916,732
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		0		0
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		187,044		174,398
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss		187,044		174,398
Commercial agency mortgage-backed securities [Member]
Schedule of Investment (Held-to-Maturity) Securities [Line Items]
Investment Securities, Gross Amortized Cost		17,258		17,258
Investment Securities, Gross Carrying Value		15,990	[1]	15,914	[2]
Investment Securities, Fair Value		14,987		15,067
Investment Securities, Gross Unrealized Gain		0		0
Investment Securities, Gross Unrealized Loss		$ (1,003)		$ (847)
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		2		2
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 0		$ 0
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		14,987		15,067
Investment Securities, Continuous Unrealized Loss Position, Fair Value		14,987		15,067
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		0		0
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		1,003		847
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss		1,003		847
Other debt securities [Member]
Schedule of Investment (Held-to-Maturity) Securities [Line Items]
Investment Securities, Gross Amortized Cost		16,288		15,787
Investment Securities, Gross Carrying Value		16,288	[1]	15,787	[2]
Investment Securities, Fair Value		14,713		14,184
Investment Securities, Gross Unrealized Gain		0		0
Investment Securities, Gross Unrealized Loss		$ (1,575)		$ (1,603)
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		3		3
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 0		$ 0
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		8,700		8,672
Investment Securities, Continuous Unrealized Loss Position, Fair Value		8,700		8,672
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		0		0
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		1,575		1,603
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss		$ 1,575		$ 1,603

[1] Carrying value includes $152 million of net unrealized loss which remains in AOCI in the Consolidated Balance Sheets related to certain securities transferred during the second quarter of 2022 from the Available for Sale securities portfolio to the Investment securities portfolio.

[2] Carrying value includes $165 million of net unrealized loss which remains in AOCI in the Consolidated Balance Sheets related to certain securities transferred during the second quarter of 2022 from the Available for Sale securities portfolio to the Investment securities portfolio.

[3] Expected maturities may differ from contractual maturities, because borrowers may have the right to call or prepay obligations with or without penalty.

[4] The average expected lives of residential mortgage-backed securities were 4.9 years based upon current prepayment assumptions.