Outstanding Commitments to Extend Credit and Letters of Credit (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Commercial, industrial, financial and agricultural
Fair Value Disclosure, Off-balance Sheet Risks, Amount, Liability	$ 3,997,401	$ 3,642,545
Real estate - home equity
Fair Value Disclosure, Off-balance Sheet Risks, Amount, Liability	1,523,494	1,475,066
Commerical mortgage and construction
Fair Value Disclosure, Off-balance Sheet Risks, Amount, Liability	1,168,624	1,188,972
Total commitments to extend credit
Fair Value Disclosure, Off-balance Sheet Risks, Amount, Liability	6,689,519	6,306,583
Standby letters of credit
Fair Value Disclosure, Off-balance Sheet Risks, Amount, Liability	303,020	309,352
Commercial letters of credit
Fair Value Disclosure, Off-balance Sheet Risks, Amount, Liability	50,432	48,682
Letter of Credit [Member]
Fair Value Disclosure, Off-balance Sheet Risks, Amount, Liability	$ 353,452	$ 358,034