Loans Loans, Loans by Credit Quality Indicator (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 20,783,069	$ 20,054,716
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	20,133,812	19,251,353
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	154,784	176,918
Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	262,585	351,142
Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	231,888	275,303
Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	6,571,000	6,489,014
Commercial and industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	6,183,037	5,937,119
Commercial and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	103,881	141,328
Commercial and industrial | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	142,607	227,196
Commercial and industrial | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	141,475	183,371
Commercial real estate — owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	845,336	897,724
Commercial real estate — owner occupied | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	754,446	805,871
Commercial real estate — owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	14,366	17,785
Commercial real estate — owner occupied | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	60,724	64,524
Commercial real estate — owner occupied | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	15,800	9,544
Commercial and business lending
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	7,416,336	7,386,738
Commercial and business lending | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	6,937,483	6,742,990
Commercial and business lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	118,247	159,113
Commercial and business lending | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	203,331	291,720
Commercial and business lending | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	157,275	192,915
Commercial real estate — investor
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	3,329,585	3,574,732
Commercial real estate — investor | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	3,260,187	3,491,217
Commercial real estate — investor | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	13,623	14,236
Commercial real estate — investor | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	48,569	51,228
Commercial real estate — investor | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	7,206	18,051
Real estate construction
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,651,805	1,432,497
Real estate construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,621,198	1,429,083
Real estate construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	19,989	105
Real estate construction | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	8,901	2,465
Real estate construction | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,717	844
Commercial real estate lending
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	4,981,390	5,007,229
Commercial real estate lending | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	4,881,385	4,920,300
Commercial real estate lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	33,612	14,341
Commercial real estate lending | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	57,470	53,693
Commercial real estate lending | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	8,923	18,895
Total commercial
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	12,397,726	12,393,967
Total commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	11,818,868	11,663,290
Total commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	151,859	173,454
Total commercial | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	260,801	345,413
Total commercial | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	166,198	211,810
Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	7,115,457	6,332,327
Residential mortgage | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	7,060,673	6,275,162
Residential mortgage | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,233	1,314
Residential mortgage | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,576	5,615
Residential mortgage | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	51,975	50,236
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	897,111	934,443
Home equity | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	882,253	919,740
Home equity | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,168	1,588
Home equity | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	208	114
Home equity | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	13,482	13,001
Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	372,775	393,979
Other consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	372,018	393,161
Other consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	524	562
Other consumer | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	0	0
Other consumer | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	233	256
Total consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	8,385,343	7,660,749
Total consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	8,314,944	7,588,063
Total consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	2,925	3,464
Total consumer | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,784	5,729
Total consumer | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 65,690	$ 63,493