Fair Value of Assets and Liabilities - Schedule of Carrying Amount, Fair Value, and Fair Value Hierarchy of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financial Instruments – Assets
Held-to-Maturity: Fair Value	$ 3,348,693	$ 3,062,882	$ 3,413,994
Carrying Amount
Financial Instruments – Assets
Held-to-Maturity: Fair Value	3,262,727	3,042,294
Loans	11,536,011	10,664,885
Financial Instruments – Liabilities
Time Deposits	1,662,063	1,802,431
Securities Sold Under Agreements to Repurchase	600,590	604,306
Other Debt	50,000	75,000
Fair Value
Financial Instruments – Assets
Held-to-Maturity: Fair Value	3,348,693	3,062,882
Loans	12,019,151	10,873,208
Financial Instruments – Liabilities
Time Deposits	1,667,774	1,800,773
Securities Sold Under Agreements to Repurchase	649,039	627,780
Other Debt	51,546	75,581
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) | Fair Value
Financial Instruments – Assets
Held-to-Maturity: Fair Value	7,500	275,663
Loans	0	0
Financial Instruments – Liabilities
Time Deposits	0	0
Securities Sold Under Agreements to Repurchase	0	0
Other Debt	0	0
Significant Other Observable Inputs (Level 2) | Fair Value
Financial Instruments – Assets
Held-to-Maturity: Fair Value	3,341,193	2,787,219
Loans	0	0
Financial Instruments – Liabilities
Time Deposits	1,667,774	1,800,773
Securities Sold Under Agreements to Repurchase	649,039	627,780
Other Debt	51,546	75,581
Significant Other Unobservable Inputs (Level 3) | Fair Value
Financial Instruments – Assets
Held-to-Maturity: Fair Value	0	0
Loans	12,019,151	10,873,208
Financial Instruments – Liabilities
Time Deposits	0	0
Securities Sold Under Agreements to Repurchase	0	0
Other Debt	$ 0	$ 0