Securities (Summary of Book Values and Fair Values of Investment Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Fair Value
Amortized Cost	$ 2,698,996	$ 2,758,556
Fair Value	2,290,265	2,314,493
Unrealized gains	3	4
Unrealized (losses)	(408,734)	(444,067)
Securities held to maturity:
Amortized Cost	539,795	541,700
Fair Value	448,904	432,528
Unrealized gains	53	7
Unrealized (losses)	(90,944)	(109,179)
U.S. Treasuries
Fair Value
Amortized Cost	174,510	174,420
Fair Value	170,109	168,758
Unrealized gains	0	0
Unrealized (losses)	(4,401)	(5,662)
Government-sponsored enterprise securities
Fair Value
Amortized Cost	71,959	71,957
Fair Value	59,304	57,456
Unrealized gains	0	0
Unrealized (losses)	(12,655)	(14,501)
Mortgage-backed securities
Fair Value
Amortized Cost	2,432,854	2,467,839
Fair Value	2,042,379	2,045,000
Unrealized gains	3	4
Unrealized (losses)	(390,478)	(422,843)
Securities held to maturity:
Amortized Cost	14,360	15,150
Fair Value	13,539	14,221
Unrealized gains	0	0
Unrealized (losses)	(821)	(929)
Corporate bonds
Fair Value
Amortized Cost	19,673	44,340
Fair Value	18,473	43,279
Unrealized gains	0	0
Unrealized (losses)	(1,200)	(1,061)
State and local governments
Securities held to maturity:
Amortized Cost	525,435	526,550
Fair Value	435,365	418,307
Unrealized gains	53	7
Unrealized (losses)	$ (90,123)	$ (108,250)