Investment Securities, Securities Held-to-Maturity (Details) - USD ($) $ in Thousands		Mar. 31, 2022	Dec. 31, 2021
Book values, estimated fair values and unrealized gains and losses of investments classified as held-to-maturity [Abstract]
Amortized cost		$ 876,257	$ 737,052
Gross unrealized gains		162	782
Gross unrealized losses		65,510	11,993
Fair value		810,909	725,841
Municipal Securities [Member]
Book values, estimated fair values and unrealized gains and losses of investments classified as held-to-maturity [Abstract]
Amortized cost		63,581	66,496
Gross unrealized gains		162	701
Gross unrealized losses		65	0
Fair value		63,678	67,197
Mortgage-backed Securities [Member]
Book values, estimated fair values and unrealized gains and losses of investments classified as held-to-maturity [Abstract]
Amortized cost	[1]	695,249	596,775
Gross unrealized gains	[1]	0	45
Gross unrealized losses	[1]	60,650	11,764
Fair value	[1]	634,599	585,056
Collateralized Mortgage Obligations [Member]
Book values, estimated fair values and unrealized gains and losses of investments classified as held-to-maturity [Abstract]
Amortized cost	[1]	117,427	73,781
Gross unrealized gains	[1]	0	36
Gross unrealized losses	[1]	4,795	229
Fair value	[1]	$ 112,632	$ 73,588

[1] All mortgage-backed securities and collateralized mortgage obligations were issued by an agency or government sponsored entity of the U.S. Government.