Loans Credit Quality Indicator (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 22,976,786	$ 20,784,991
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	22,331,647	20,171,876
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	199,162	227,692
Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	241,517	176,877
Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	204,460	208,546
Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans	7,109,796	6,399,693
Commercial and industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	6,763,557	6,015,884
Commercial and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	92,286	157,245
Commercial and industrial | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	172,177	113,778
Commercial and industrial | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	81,776	112,786
Commercial real estate — owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans	888,330	802,209
Commercial real estate — owner occupied | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	814,769	723,291
Commercial real estate — owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	16,033	14,181
Commercial real estate — owner occupied | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	38,879	41,997
Commercial real estate — owner occupied | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	18,649	22,740
Commercial and business lending
Financing Receivable, Recorded Investment [Line Items]
Loans	7,998,126	7,201,902
Commercial and business lending | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	7,578,326	6,739,175
Commercial and business lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	108,319	171,426
Commercial and business lending | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	211,056	155,775
Commercial and business lending | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	100,425	135,526
Commercial real estate — investor
Financing Receivable, Recorded Investment [Line Items]
Loans	3,996,415	3,315,254
Commercial real estate — investor | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	3,885,535	3,266,389
Commercial real estate — investor | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	59,587	24,845
Commercial real estate — investor | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	24,790	19,291
Commercial real estate — investor | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	26,503	4,729
Real estate construction
Financing Receivable, Recorded Investment [Line Items]
Loans	1,487,159	1,451,684
Real estate construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	1,452,888	1,421,504
Real estate construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	29,559	29,206
Real estate construction | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	3,168	0
Real estate construction | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	1,544	974
Commercial real estate lending
Financing Receivable, Recorded Investment [Line Items]
Loans	5,483,574	4,766,938
Commercial real estate lending | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	5,338,423	4,687,893
Commercial real estate lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	89,146	54,051
Commercial real estate lending | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	27,958	19,291
Commercial real estate lending | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	28,047	5,703
Total commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	13,481,700	11,968,840
Total commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	12,916,749	11,427,068
Total commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	197,465	225,477
Total commercial | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	239,014	175,066
Total commercial | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	128,472	141,229
Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans	8,207,253	7,546,534
Residential mortgage | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	8,141,803	7,490,860
Residential mortgage | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	199	426
Residential mortgage | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	2,355	1,616
Residential mortgage | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	62,896	53,632
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	911,363	883,804
Home equity | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	897,471	868,958
Home equity | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	792	1,137
Home equity | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	142	195
Home equity | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	12,958	13,514
Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	376,470	385,813
Other consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	375,624	384,990
Other consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	706	652
Other consumer | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	6	0
Other consumer | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	134	171
Total consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	9,495,086	8,816,151
Total consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	9,414,898	8,744,808
Total consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	1,697	2,215
Total consumer | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	2,503	1,811
Total consumer | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 75,988	$ 67,317