Securities Securities - Amortized Cost, Allowance for Credit Losses and Estimated Fair Value of Securities Held to Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	$ 1,665,623	$ 1,749,337
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	3,622	59,907
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	29,252	101
Debt Securities, Held-to-maturity, Fair Value	1,639,993	1,809,143
Securities, held-to-maturity, allowance for credit loss	(158)	(158)
Securities held to maturity, net of allowance for credit losses of $158 at March 31, 2022 and $158 at December 31, 2021	1,665,465	1,749,179
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	526,969	527,264
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0	18,766
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	17,519	0
Debt Securities, Held-to-maturity, Fair Value	509,450	546,030
Securities, held-to-maturity, allowance for credit loss	0	0
Securities held to maturity, net of allowance for credit losses of $158 at March 31, 2022 and $158 at December 31, 2021	526,969	527,264
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	1,137,154	1,220,573
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	3,622	41,141
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	11,717	101
Debt Securities, Held-to-maturity, Fair Value	1,129,059	1,261,613
Securities, held-to-maturity, allowance for credit loss	(158)	(158)
Securities held to maturity, net of allowance for credit losses of $158 at March 31, 2022 and $158 at December 31, 2021	1,136,996	1,220,415
Other Investments [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	1,500	1,500
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0	0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	16	0
Debt Securities, Held-to-maturity, Fair Value	1,484	1,500
Securities, held-to-maturity, allowance for credit loss	0	0
Securities held to maturity, net of allowance for credit losses of $158 at March 31, 2022 and $158 at December 31, 2021	$ 1,500	$ 1,500