Investment Securities - Summary of Available-for-Sale Debt Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Available-for-sale debt securities:
Amortized Cost	$ 3,614,342	$ 3,572,482
Gross Unrealized Gains	19,768	540
Gross Unrealized Losses	(115,448)	(347,130)
Estimated Fair Value	3,518,662	3,225,892
Held-to-maturity debt securities:
Held-to-maturity debt securities	812,432	865,477
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(84,689)	(101,633)
Estimated Fair Value	727,743	763,844
Equity securities at fair value	74,426	51,825
Total investment securities	4,405,520	4,143,194
Interest receivable	114,800	118,100
Available-for-sale
Available-for-sale debt securities:
Amortized Cost	3,614,342
Estimated Fair Value	3,518,662
Held-to-maturity debt securities:
Interest receivable	13,900	9,500
Held-to-maturity
Held-to-maturity debt securities:
Estimated Fair Value	727,743
Interest receivable	1,300	1,400
U.S. Treasury securities
Available-for-sale debt securities:
Amortized Cost	278,200	651,112
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2,396)	(14,639)
Estimated Fair Value	275,804	636,473
U.S. government agency securities
Available-for-sale debt securities:
Amortized Cost		125,000
Gross Unrealized Gains		0
Gross Unrealized Losses		(18,408)
Estimated Fair Value		106,592
Residential mortgage-backed securities
Available-for-sale debt securities:
Amortized Cost	3,323,351	2,782,734
Gross Unrealized Gains	19,768	540
Gross Unrealized Losses	(112,263)	(312,442)
Estimated Fair Value	3,230,856	2,470,832
Held-to-maturity debt securities:
Held-to-maturity debt securities	812,432	865,477
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(84,689)	(101,633)
Estimated Fair Value	727,743	763,844
CRT securities
Available-for-sale debt securities:
Amortized Cost	12,791	13,636
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(789)	(1,641)
Estimated Fair Value	$ 12,002	$ 11,995

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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