Securities (Summary of Book Values and Fair Values of Investment Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Fair Value
Amortized Cost	$ 2,898,910	$ 2,662,481
Fair Value	2,685,048	2,630,414
Unrealized Gains	716	10,595
Unrealized (Losses)	(214,578)	(42,662)
Securities held to maturity:
Amortized Cost	546,090	513,825
Fair Value	492,307	511,699
Unrealized Gains	20	3,540
Unrealized (Losses)	(53,803)	(5,666)
US Treasuries
Fair Value
Amortized Cost	149,534	0
Fair Value	149,391	0
Unrealized Gains	0	0
Unrealized (Losses)	(143)	0
Government-sponsored enterprise securities
Fair Value
Amortized Cost	71,953	71,951
Fair Value	64,168	69,179
Unrealized Gains	0	0
Unrealized (Losses)	(7,785)	(2,772)
Mortgage-backed securities
Fair Value
Amortized Cost	2,632,054	2,545,150
Fair Value	2,425,911	2,514,805
Unrealized Gains	349	9,489
Unrealized (Losses)	(206,492)	(39,834)
Securities held to maturity:
Amortized Cost	18,662	20,260
Fair Value	18,513	20,845
Unrealized Gains	1	585
Unrealized (Losses)	(150)	0
Corporate bonds
Fair Value
Amortized Cost	45,369	45,380
Fair Value	45,578	46,430
Unrealized Gains	367	1,106
Unrealized (Losses)	(158)	(56)
State and local governments
Securities held to maturity:
Amortized Cost	527,428	493,565
Fair Value	473,794	490,854
Unrealized Gains	19	2,955
Unrealized (Losses)	$ (53,653)	$ (5,666)

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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