Loans and Allowance for Credit Losses, Loans by Portfolio Type (Details) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest		$ 6,136,400	$ 5,749,373
Loans, variable rate of interest		15,976,501	15,744,110
Loans, non-accrual		172,466	163,247
Total		22,285,367	21,656,730
Accruing loans past due (90 days)	[1]	1,541	1,338
Credit Commitments [Abstract]
Outstanding commitments to extend credit		11,000,000
Outstanding standby letters of credit		713,000
Commercial [Member]
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest		3,184,237	2,251,188
Loans, variable rate of interest		11,128,682	11,285,049
Loans, non-accrual		111,706	99,841
Total		14,424,625	13,636,078
Commercial real estate [Member]
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest		1,070,050	1,477,274
Loans, variable rate of interest		3,532,822	3,265,918
Loans, non-accrual		23,185	21,621
Total		4,626,057	4,764,813
Residential mortgage [Member]
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest		1,690,286	1,830,224
Loans, variable rate of interest		389,713	358,254
Loans, non-accrual		37,304	41,555
Total		2,117,303	2,230,033
Personal [Member]
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest		191,827	190,687
Loans, variable rate of interest		925,284	834,889
Loans, non-accrual		271	230
Total		$ 1,117,382	$ 1,025,806

[1] Excludes residential mortgage loans guaranteed by agencies of the U.S. government