Loans Credit Quality Indicator (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 22,867,112	$ 20,784,991
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	22,313,389	20,171,876
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	163,182	227,692
Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	236,449	176,877
Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	154,092	208,546
Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans	7,159,941	6,399,693
Commercial and industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	6,886,363	6,015,884
Commercial and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	78,964	157,245
Commercial and industrial | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	144,468	113,778
Commercial and industrial | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	50,146	112,786
Commercial real estate — owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans	867,682	802,209
Commercial real estate — owner occupied | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	823,615	723,291
Commercial real estate — owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	6,762	14,181
Commercial real estate — owner occupied | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	32,526	41,997
Commercial real estate — owner occupied | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	4,779	22,740
Commercial and business lending
Financing Receivable, Recorded Investment [Line Items]
Loans	8,027,622	7,201,902
Commercial and business lending | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	7,709,978	6,739,175
Commercial and business lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	85,725	171,426
Commercial and business lending | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	176,994	155,775
Commercial and business lending | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	54,925	135,526
Commercial real estate — investor
Financing Receivable, Recorded Investment [Line Items]
Loans	3,924,499	3,315,254
Commercial real estate — investor | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	3,790,423	3,266,389
Commercial real estate — investor | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	64,509	24,845
Commercial real estate — investor | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	49,842	19,291
Commercial real estate — investor | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	19,725	4,729
Real estate construction
Financing Receivable, Recorded Investment [Line Items]
Loans	1,416,209	1,451,684
Real estate construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	1,401,585	1,421,504
Real estate construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	10,078	29,206
Real estate construction | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	3,392	0
Real estate construction | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	1,154	974
Commercial real estate lending
Financing Receivable, Recorded Investment [Line Items]
Loans	5,340,708	4,766,938
Commercial real estate lending | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	5,192,008	4,687,893
Commercial real estate lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	74,587	54,051
Commercial real estate lending | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	53,234	19,291
Commercial real estate lending | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	20,879	5,703
Total commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	13,368,330	11,968,840
Total commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	12,901,986	11,427,068
Total commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	160,312	225,477
Total commercial | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	230,228	175,066
Total commercial | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	75,804	141,229
Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans	8,227,649	7,546,534
Residential mortgage | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	8,154,521	7,490,860
Residential mortgage | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	1,159	426
Residential mortgage | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	6,073	1,616
Residential mortgage | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	65,896	53,632
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	901,275	883,804
Home equity | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	887,690	868,958
Home equity | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	1,113	1,137
Home equity | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	148	195
Home equity | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	12,324	13,514
Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	369,858	385,813
Other consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	369,192	384,990
Other consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	598	652
Other consumer | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Other consumer | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	68	171
Total consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	9,498,782	8,816,151
Total consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	9,411,403	8,744,808
Total consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	2,870	2,215
Total consumer | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	6,221	1,811
Total consumer | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 78,288	$ 67,317