Loans and Allowance for Credit Losses, Loans by Portfolio Type (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest		$ 6,206,884	$ 5,749,373
Loans, variable rate of interest		15,864,989	15,744,110
Loans, non-accrual		183,779	163,247
Total		22,255,652	21,656,730
Accruing loans past due (90 days)	[1]	2,698	1,338
Credit Commitments [Abstract]
Outstanding commitments to extend credit		11,000,000
Outstanding standby letters of credit		699,000
Commercial [Member]
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest		3,264,990	2,251,188
Loans, variable rate of interest		10,948,523	11,285,049
Loans, non-accrual		123,395	99,841
Total		14,336,908	13,636,078
Commercial real estate [Member]
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest		1,008,236	1,477,274
Loans, variable rate of interest		3,680,127	3,265,918
Loans, non-accrual		21,670	21,621
Total		4,710,033	4,764,813
Residential mortgage [Member]
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest		1,751,803	1,830,224
Loans, variable rate of interest		380,542	358,254
Loans, non-accrual		38,477	41,555
Total		2,170,822	2,230,033
Personal [Member]
Loan receivables disclosure [Abstract]
Loans, fixed rate of interest		181,855	190,687
Loans, variable rate of interest		855,797	834,889
Loans, non-accrual		237	230
Total		$ 1,037,889	$ 1,025,806

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