Securities (Summary of Book Values and Fair Values of Investment Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Fair Value
Amortized Cost	$ 2,507,371	$ 2,590,099
Fair Value	2,088,483	2,189,379
Unrealized gains	22	30
Unrealized (losses)	(418,910)	(400,750)
Securities held to maturity:
Amortized Cost	525,627	533,678
Fair Value	436,655	449,623
Unrealized gains	5	39
Unrealized (losses)	(88,977)	(84,094)
U.S. Treasuries
Fair Value
Amortized Cost	124,876	174,785
Fair Value	123,770	172,570
Unrealized gains	0	0
Unrealized (losses)	(1,106)	(2,215)
Government-sponsored enterprise securities
Fair Value
Amortized Cost	71,965	71,964
Fair Value	59,959	60,266
Unrealized gains	0	0
Unrealized (losses)	(12,006)	(11,698)
Mortgage-backed securities
Fair Value
Amortized Cost	2,291,854	2,323,674
Fair Value	1,886,949	1,937,784
Unrealized gains	22	30
Unrealized (losses)	(404,927)	(385,920)
Securities held to maturity:
Amortized Cost	11,369	12,085
Fair Value	10,682	11,447
Unrealized gains	0	0
Unrealized (losses)	(687)	(638)
Corporate bonds
Fair Value
Amortized Cost	18,676	19,676
Fair Value	17,805	18,759
Unrealized gains	0	0
Unrealized (losses)	(871)	(917)
State and local governments
Securities held to maturity:
Amortized Cost	514,258	521,593
Fair Value	425,973	438,176
Unrealized gains	5	39
Unrealized (losses)	$ (88,290)	$ (83,456)

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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Amount, before tax, of unrealized loss 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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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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