Investment Securities - Securities Held-to-Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2023		Jun. 30, 2023	Dec. 31, 2022		Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, before Allowance for Credit Loss	$ 2,284,086	[1]		$ 2,270,635	[2]
Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest	(1,500)	[1]	$ (1,500)	(1,500)	[2]	$ (1,500)	$ (1,500)	$ 0
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, after Allowance for Credit Loss, Total	2,282,586	[1]		2,269,135	[2]
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0	[1]		8	[2]
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(269,291)	[1]		(158,671)	[2]
Debt Securities, Held-to-maturity, Fair Value	2,013,295	[1]		2,110,472	[2]
Municipal securities
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, before Allowance for Credit Loss	1,246,249			1,243,443
Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest	(140)			(140)
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, after Allowance for Credit Loss, Total	1,246,109			1,243,303
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0			8
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(128,038)			(77,526)
Debt Securities, Held-to-maturity, Fair Value	1,118,071			1,165,785
Agency commercial MBS
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, before Allowance for Credit Loss	432,191			427,411
Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest	0			0
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, after Allowance for Credit Loss, Total	432,191			427,411
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0			0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(53,609)			(34,287)
Debt Securities, Held-to-maturity, Fair Value	378,582			393,124
Private label commercial MBS
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, before Allowance for Credit Loss	349,296			345,825
Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest	0			0
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, after Allowance for Credit Loss, Total	349,296			345,825
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0			0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(46,634)			(26,027)
Debt Securities, Held-to-maturity, Fair Value	302,662			319,798
U.S. Treasury securities
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, before Allowance for Credit Loss	186,308			184,162
Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest	0			0
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, after Allowance for Credit Loss, Total	186,308			184,162
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0			0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(20,645)			(12,462)
Debt Securities, Held-to-maturity, Fair Value	165,663			171,700
Corporate Debt Securities
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, before Allowance for Credit Loss	70,042			69,794
Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest	(1,360)			(1,360)
Debt Securities, Held-to-Maturity, Excluding Accrued Interest, after Allowance for Credit Loss, Total	68,682			68,434
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0			0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(20,365)			(8,369)
Debt Securities, Held-to-maturity, Fair Value	48,317			60,065
Interest Receivable	$ 11,300			$ 13,500

[1] Excludes accrued interest receivable of $11.3 million at September 30, 2023 which is recorded in "Other assets" on the condensed consolidated balance sheets

[2] Excludes accrued interest receivable of $13.5 million at December 31, 2022 which is recorded in "Other assets" on the condensed consolidated balance sheets