Investment Securities - Amortized Cost and Fair Value of Available for Sale Securities and Held to Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Amortized Cost
Due in one year or less	$ 6,240	$ 6,954
Due after one through five years	6,106	5,097
Due after five through ten years	135,605	120,460
Due after ten years	1,487,507	1,464,460
Total debt securities with a single maturity date	1,635,458	1,596,971
Total investment securities	2,265,457	2,268,655
Fair Value
Due in one year or less	6,189	6,965
Due after one through five years	6,128	5,309
Due after five through ten years	135,384	126,816
Due after ten years	1,433,972	1,537,856
Total debt securities with a single maturity date	1,581,673	1,676,946
Total investment securities	2,164,197	2,344,551
Amortized Cost
Due in one year or less	7,718	6,971
Due after one through five years	30,156	30,272
Due after five through ten years	179,256	177,203
Due after ten years	1,266,753	1,215,812
Total debt securities with a single maturity date	1,483,883	1,430,258
Amortized Cost	2,325,311	2,180,047
Fair Value
Due in one year or less	7,737	6,995
Due after one through five years	30,777	31,946
Due after five through ten years	173,697	180,129
Due after ten years	1,141,661	1,231,568
Total debt securities with a single maturity date	1,353,872	1,450,638
Investment securities held to maturity	2,145,994	2,202,503
U.S. Government-sponsored mortgage-backed securities
Amortized Cost
Without single maturity date	629,999	671,684
Fair Value
Without single maturity date	582,524	667,605
Total investment securities	582,524	667,605
Amortized Cost
Without single maturity date	841,428	749,789
Amortized Cost	841,428	749,789
Fair Value
Without single maturity date	792,122	751,865
Investment securities held to maturity	$ 792,122	$ 751,865