Loans Loans, Loans by Credit Quality Indicator (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 19,815,286	$ 18,714,343
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	18,788,181	17,804,216
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	287,769	430,152
Potential Problem [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	456,734	301,717
Nonaccrual Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	282,602	178,258
Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	6,701,986	6,190,683
Commercial and industrial | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	5,910,730	5,522,809
Commercial and industrial | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	217,999	341,169
Commercial and industrial | Potential Problem [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	379,818	233,130
Commercial and industrial | Nonaccrual Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	193,439	93,575
Commercial real estate — owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	921,736	918,212
Commercial real estate — owner occupied | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	826,327	835,572
Commercial real estate — owner occupied | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	40,103	38,885
Commercial real estate — owner occupied | Potential Problem [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	45,671	35,706
Commercial real estate — owner occupied | Nonaccrual Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	9,635	8,049
Commercial and business lending
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	7,623,722	7,108,895
Commercial and business lending | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	6,737,057	6,358,381
Commercial and business lending | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	258,102	380,054
Commercial and business lending | Potential Problem [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	425,489	268,836
Commercial and business lending | Nonaccrual Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	203,074	101,624
Commercial real estate — investor
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	3,495,791	3,234,266
Commercial real estate — investor | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	3,436,680	3,153,703
Commercial real estate — investor | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	22,502	45,976
Commercial real estate — investor | Potential Problem [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	25,081	25,944
Commercial real estate — investor | Nonaccrual Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	11,528	8,643
Real estate construction
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,285,573	1,162,145
Real estate construction | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,281,526	1,157,034
Real estate construction | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	973	252
Real estate construction | Potential Problem [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	2,117	3,919
Real estate construction | Nonaccrual Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	957	940
Commercial real estate lending
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	4,781,364	4,396,411
Commercial real estate lending | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	4,718,206	4,310,737
Commercial real estate lending | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	23,475	46,228
Commercial real estate lending | Potential Problem [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	27,198	29,863
Commercial real estate lending | Nonaccrual Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	12,485	9,583
Total commercial
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	12,405,086	11,505,306
Total commercial | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	11,455,263	10,669,118
Total commercial | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	281,577	426,282
Total commercial | Potential Problem [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	452,687	298,699
Total commercial | Nonaccrual Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	215,559	111,207
Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	6,035,720	5,783,267
Residential mortgage | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	5,975,297	5,727,437
Residential mortgage | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	4,170	1,552
Residential mortgage | Potential Problem [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	3,953	2,796
Residential mortgage | Nonaccrual Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	52,300	51,482
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	968,771	1,005,802
Home equity | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	952,727	988,574
Home equity | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,587	1,762
Home equity | Potential Problem [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	94	222
Home equity | Nonaccrual Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	14,363	15,244
Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	405,709	419,968
Other consumer | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	404,894	419,087
Other consumer | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	435	556
Other consumer | Potential Problem [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	0	0
Other consumer | Nonaccrual Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	380	325
Total consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	7,410,200	7,209,037
Total consumer | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	7,332,918	7,135,098
Total consumer | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	6,192	3,870
Total consumer | Potential Problem [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	4,047	3,018
Total consumer | Nonaccrual Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 67,043	$ 67,051