Securities (Summary of Book Values and Fair Values of Investment Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value
Amortized Cost	$ 1,825,484	$ 1,432,684
Fair Value	1,821,697	1,453,132
Unrealized Gains	18,581	22,963
Unrealized (Losses)	(22,368)	(2,515)
Debt Securities, Held-to-maturity, Maturity [Abstract]
Amortized Cost	198,843	167,551
Fair Value	195,424	170,734
Unrealized Gains	1,432	3,348
Unrealized (Losses)	(4,851)	(165)
Government-sponsored enterprise securities
Fair Value
Amortized Cost	70,015	70,016
Fair Value	67,022	70,206
Unrealized Gains	0	371
Unrealized (Losses)	(2,993)	(181)
Mortgage-backed securities
Fair Value
Amortized Cost	1,711,809	1,318,998
Fair Value	1,709,811	1,337,706
Unrealized Gains	17,167	20,832
Unrealized (Losses)	(19,165)	(2,124)
Debt Securities, Held-to-maturity, Maturity [Abstract]
Amortized Cost	26,977	29,959
Fair Value	27,999	30,900
Unrealized Gains	1,022	941
Unrealized (Losses)	0	0
Corporate bonds
Fair Value
Amortized Cost	43,660	43,670
Fair Value	44,864	45,220
Unrealized Gains	1,414	1,760
Unrealized (Losses)	(210)	(210)
State and local governments
Debt Securities, Held-to-maturity, Maturity [Abstract]
Amortized Cost	171,866	137,592
Fair Value	167,425	139,834
Unrealized Gains	410	2,407
Unrealized (Losses)	$ (4,851)	$ (165)

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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