Investment Securities - Unrealized Gross Losses and Fair Values of Securities in a Continuous Loss Position (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024 USD ($) security shares	Dec. 31, 2023 USD ($) security shares	Dec. 31, 2016 shares
Securities in the available-for-sale portfolio in a continuous loss position
Number of individual securities in a continuous loss position | security	204	222
Time in Continuous Loss, Unrealized Losses
Less Than 12 Months Unrealized Losses	$ (8)	$ (564)
12 Months or More Unrealized Losses	(307,288)	(302,818)
Total Unrealized Losses	(307,296)	(303,382)
Time in Continuous Loss, Fair Value
Less Than 12 Months, Fair Value	8,492	63,667
12 Months or More Fair Value	1,996,581	2,170,608
Total Fair Value	2,005,073	2,234,275
Allowance for credit losses, investment securities	$ 0	$ 0
Investment securities comprised of collateralized loan obligations rated AA or better and obligations issued by local state and political subdivisions rated AA or better	5.00%	5.00%
Class B restricted shares
Time in Continuous Loss, Fair Value
Net realized gain		$ 40,800
Shares held | shares	0	0
Number of shares sold | shares		120,000
Class B restricted shares | Visa
Time in Continuous Loss, Fair Value
Number of shares sold | shares			274,000
U.S. Treasury and government agency debt securities
Time in Continuous Loss, Unrealized Losses
12 Months or More Unrealized Losses	$ (433)	$ (666)
Total Unrealized Losses	(433)	(666)
Time in Continuous Loss, Fair Value
12 Months or More Fair Value	12,821	32,503
Total Fair Value	12,821	32,503
Government-sponsored enterprises debt securities
Time in Continuous Loss, Unrealized Losses
12 Months or More Unrealized Losses	(371)	(408)
Total Unrealized Losses	(371)	(408)
Time in Continuous Loss, Fair Value
12 Months or More Fair Value	19,629	19,592
Total Fair Value	19,629	19,592
Residential - Government-sponsored enterprises
Time in Continuous Loss, Unrealized Losses
12 Months or More Unrealized Losses	(114,648)	(112,124)
Total Unrealized Losses	(114,648)	(112,124)
Time in Continuous Loss, Fair Value
12 Months or More Fair Value	753,385	783,297
Total Fair Value	753,385	783,297
Residential - Government agency
Time in Continuous Loss, Unrealized Losses
12 Months or More Unrealized Losses	(1,350)	(1,121)
Total Unrealized Losses	(1,350)	(1,121)
Time in Continuous Loss, Fair Value
12 Months or More Fair Value	9,609	10,182
Total Fair Value	9,609	10,182
Commercial - Government agency
Time in Continuous Loss, Unrealized Losses
12 Months or More Unrealized Losses	(51,297)	(50,270)
Total Unrealized Losses	(51,297)	(50,270)
Time in Continuous Loss, Fair Value
12 Months or More Fair Value	213,394	218,674
Total Fair Value	213,394	218,674
Commercial - Government-sponsored enterprises
Time in Continuous Loss, Unrealized Losses
12 Months or More Unrealized Losses	(6,951)	(7,028)
Total Unrealized Losses	(6,951)	(7,028)
Time in Continuous Loss, Fair Value
12 Months or More Fair Value	83,490	86,431
Total Fair Value	83,490	86,431
Commercial - Non -agency
Time in Continuous Loss, Unrealized Losses
12 Months or More Unrealized Losses		(281)
Total Unrealized Losses		(281)
Time in Continuous Loss, Fair Value
12 Months or More Fair Value		21,683
Total Fair Value		21,683
Government agency
Time in Continuous Loss, Unrealized Losses
12 Months or More Unrealized Losses	(70,997)	(67,568)
Total Unrealized Losses	(70,997)	(67,568)
Time in Continuous Loss, Fair Value
12 Months or More Fair Value	452,163	471,150
Total Fair Value	452,163	471,150
Government-sponsored enterprises
Time in Continuous Loss, Unrealized Losses
12 Months or More Unrealized Losses	(60,670)	(61,856)
Total Unrealized Losses	(60,670)	(61,856)
Time in Continuous Loss, Fair Value
12 Months or More Fair Value	353,061	363,970
Total Fair Value	353,061	363,970
Collateralized Loan Obligations
Time in Continuous Loss, Unrealized Losses
Less Than 12 Months Unrealized Losses	(8)	(564)
12 Months or More Unrealized Losses	(571)	(1,496)
Total Unrealized Losses	(579)	(2,060)
Time in Continuous Loss, Fair Value
Less Than 12 Months, Fair Value	8,492	63,667
12 Months or More Fair Value	99,029	163,126
Total Fair Value	$ 107,521	$ 226,793