Loans and Allowance for Credit Losses, Loans by Portfolio Type (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest	$ 6,129,401	$ 6,134,362
Loans, variable rate of interest	16,171,397	15,435,674
Loans, non-accrual	163,172	180,951
Total	22,463,970	21,750,987
Past Due 90 Days or More and Accruing	100,686	7,680
Credit Commitments [Abstract]
Outstanding commitments to extend credit	10,000,000
Outstanding standby letters of credit	684,000
Commercial [Member]
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest	3,205,558	3,231,485
Loans, variable rate of interest	11,471,793	10,684,749
Loans, non-accrual	118,624	115,416
Total	14,795,975	14,031,650
Past Due 90 Days or More and Accruing	788
Commercial real estate [Member]
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest	1,045,825	1,056,321
Loans, variable rate of interest	3,395,715	3,349,836
Loans, non-accrual	8,545	27,626
Total	4,450,085	4,433,783
Past Due 90 Days or More and Accruing	2,796
Loans to individuals [Member]
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest	1,878,018
Loans, variable rate of interest	1,303,889
Loans, non-accrual	36,003
Total	3,217,910	2,084,172
Past Due 90 Days or More and Accruing	97,102
Loans to individuals [Member] | Residential mortgage [Member]
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest		1,652,653
Loans, variable rate of interest		393,897
Loans, non-accrual		37,622
Total	1,844,555	2,084,172
Past Due 90 Days or More and Accruing	119
Loans to individuals [Member] | Personal [Member]
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest		193,903
Loans, variable rate of interest		1,007,192
Loans, non-accrual		287
Total	1,175,466	$ 1,201,382
Past Due 90 Days or More and Accruing	$ 3