Investment Securities - Amortized Cost and Fair Value of Available for Sale Securities and Held to Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Amortized Cost
Due in one year or less	$ 6,707	$ 6,954
Due after one through five years	28,721	5,097
Due after five through ten years	164,626	120,460
Due after ten years	1,630,162	1,464,460
Total debt securities with a single maturity date	1,830,216	1,596,971
Total investment securities	2,542,432	2,268,655
Fair Value
Due in one year or less	6,664	6,965
Due after one through five years	28,420	5,309
Due after five through ten years	159,497	126,816
Due after ten years	1,465,311	1,537,856
Total debt securities with a single maturity date	1,659,892	1,676,946
Total investment securities	2,296,351	2,344,551
Amortized Cost
Due in one year or less	5,591	6,971
Due after one through five years	41,180	30,272
Due after five through ten years	174,108	177,203
Due after ten years	1,291,478	1,215,812
Total debt securities with a single maturity date	1,512,357	1,430,258
Amortized Cost	2,333,924	2,180,047
Fair Value
Due in one year or less	5,604	6,995
Due after one through five years	41,092	31,946
Due after five through ten years	163,070	180,129
Due after ten years	1,073,029	1,231,568
Total debt securities with a single maturity date	1,282,795	1,450,638
Investment securities held to maturity	2,025,524	2,202,503
U.S. Government-sponsored mortgage-backed securities
Amortized Cost
Without single maturity date	712,216	671,684
Fair Value
Without single maturity date	636,459	667,605
Total investment securities	636,459	667,605
Amortized Cost
Without single maturity date	821,567	749,789
Amortized Cost	821,567	749,789
Fair Value
Without single maturity date	742,729	751,865
Investment securities held to maturity	$ 742,729	$ 751,865