Loans, Loans by Past Due Status (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Summarized details of Loans
Current	$ 18,923,228	$ 18,510,978
Financing Receivable, Recorded Investment, Nonaccrual Status	286,395	178,258
Total loans	19,227,240	18,714,343
Accruing loans past due 90 days or more	2,000	2,000
Nonaccrual Loans, Current Portion	$ 230,000	$ 124,000
Percent of current nonaccrual loans	80.00%	69.00%
Financing Receivables, 30 to 59 Days Past Due [Member]
Summarized details of Loans
Total Past Due	$ 12,977	$ 20,181
Financing Receivables, 60 to 89 Days Past Due [Member]
Summarized details of Loans
Total Past Due	3,011	3,278
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Summarized details of Loans
Total Past Due	1,629	1,648
Commercial and industrial
Summarized details of Loans
Current	6,311,415	6,095,848
Financing Receivable, Recorded Investment, Nonaccrual Status	197,115	93,575
Total loans	6,511,648	6,190,683
Commercial and industrial | Financing Receivables, 30 to 59 Days Past Due [Member]
Summarized details of Loans
Total Past Due	2,665	602
Commercial and industrial | Financing Receivables, 60 to 89 Days Past Due [Member]
Summarized details of Loans
Total Past Due	236	409
Commercial and industrial | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Summarized details of Loans
Total Past Due	217	249
Commercial real estate — owner occupied
Summarized details of Loans
Current	907,322	903,021
Financing Receivable, Recorded Investment, Nonaccrual Status	9,443	8,049
Total loans	917,285	918,212
Commercial real estate — owner occupied | Financing Receivables, 30 to 59 Days Past Due [Member]
Summarized details of Loans
Total Past Due	520	7,142
Commercial real estate — owner occupied | Financing Receivables, 60 to 89 Days Past Due [Member]
Summarized details of Loans
Total Past Due	0	0
Commercial real estate — owner occupied | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Summarized details of Loans
Total Past Due	0	0
Commercial and business lending
Summarized details of Loans
Current	7,218,737	6,998,869
Financing Receivable, Recorded Investment, Nonaccrual Status	206,558	101,624
Total loans	7,428,933	7,108,895
Commercial and business lending | Financing Receivables, 30 to 59 Days Past Due [Member]
Summarized details of Loans
Total Past Due	3,185	7,744
Commercial and business lending | Financing Receivables, 60 to 89 Days Past Due [Member]
Summarized details of Loans
Total Past Due	236	409
Commercial and business lending | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Summarized details of Loans
Total Past Due	217	249
Commercial real estate — investor
Summarized details of Loans
Current	3,263,331	3,225,332
Financing Receivable, Recorded Investment, Nonaccrual Status	12,330	8,643
Total loans	3,276,733	3,234,266
Commercial real estate — investor | Financing Receivables, 30 to 59 Days Past Due [Member]
Summarized details of Loans
Total Past Due	748	291
Commercial real estate — investor | Financing Receivables, 60 to 89 Days Past Due [Member]
Summarized details of Loans
Total Past Due	324	0
Commercial real estate — investor | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Summarized details of Loans
Total Past Due	0	0
Real estate construction
Summarized details of Loans
Current	1,183,143	1,160,909
Financing Receivable, Recorded Investment, Nonaccrual Status	840	940
Total loans	1,184,398	1,162,145
Real estate construction | Financing Receivables, 30 to 59 Days Past Due [Member]
Summarized details of Loans
Total Past Due	415	270
Real estate construction | Financing Receivables, 60 to 89 Days Past Due [Member]
Summarized details of Loans
Total Past Due	0	26
Real estate construction | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Summarized details of Loans
Total Past Due	0	0
Commercial Real Estate Lending [Member]
Summarized details of Loans
Current	4,446,474	4,386,241
Financing Receivable, Recorded Investment, Nonaccrual Status	13,170	9,583
Total loans	4,461,131	4,396,411
Commercial Real Estate Lending [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Summarized details of Loans
Total Past Due	1,163	561
Commercial Real Estate Lending [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Summarized details of Loans
Total Past Due	324	26
Commercial Real Estate Lending [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Summarized details of Loans
Total Past Due	0	0
Commercial Financing Receivable [Member]
Summarized details of Loans
Current	11,665,211	11,385,110
Financing Receivable, Recorded Investment, Nonaccrual Status	219,728	111,207
Total loans	11,890,064	11,505,306
Commercial Financing Receivable [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Summarized details of Loans
Total Past Due	4,348	8,305
Commercial Financing Receivable [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Summarized details of Loans
Total Past Due	560	435
Commercial Financing Receivable [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Summarized details of Loans
Total Past Due	217	249
Residential mortgage
Summarized details of Loans
Current	5,888,651	5,726,855
Financing Receivable, Recorded Investment, Nonaccrual Status	52,212	51,482
Total loans	5,944,457	5,783,267
Residential mortgage | Financing Receivables, 30 to 59 Days Past Due [Member]
Summarized details of Loans
Total Past Due	3,199	4,491
Residential mortgage | Financing Receivables, 60 to 89 Days Past Due [Member]
Summarized details of Loans
Total Past Due	395	439
Residential mortgage | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Summarized details of Loans
Total Past Due	0	0
Home equity
Summarized details of Loans
Current	963,118	982,639
Financing Receivable, Recorded Investment, Nonaccrual Status	14,072	15,244
Total loans	982,994	1,005,802
Home equity | Financing Receivables, 30 to 59 Days Past Due [Member]
Summarized details of Loans
Total Past Due	4,410	6,190
Home equity | Financing Receivables, 60 to 89 Days Past Due [Member]
Summarized details of Loans
Total Past Due	1,394	1,729
Home equity | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Summarized details of Loans
Total Past Due	0	0
Other consumer
Summarized details of Loans
Current	406,248	416,374
Financing Receivable, Recorded Investment, Nonaccrual Status	383	325
Total loans	409,725	419,968
Other consumer | Financing Receivables, 30 to 59 Days Past Due [Member]
Summarized details of Loans
Total Past Due	1,020	1,195
Other consumer | Financing Receivables, 60 to 89 Days Past Due [Member]
Summarized details of Loans
Total Past Due	662	675
Other consumer | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Summarized details of Loans
Total Past Due	1,412	1,399
Consumer Loan [Member]
Summarized details of Loans
Current	7,258,017	7,125,868
Financing Receivable, Recorded Investment, Nonaccrual Status	66,667	67,051
Total loans	7,337,176	7,209,037
Consumer Loan [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Summarized details of Loans
Total Past Due	8,629	11,876
Consumer Loan [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Summarized details of Loans
Total Past Due	2,451	2,843
Consumer Loan [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Summarized details of Loans
Total Past Due	$ 1,412	$ 1,399