Loans - Credit Quality Indicator (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 22,810,491	$ 20,784,991
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	22,080,128	20,171,876
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	239,626	227,692
Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	282,184	176,877
Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	208,553	208,546
Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans	6,756,983	6,399,693
Commercial and industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	6,325,258	6,015,884
Commercial and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	132,292	157,245
Commercial and industrial | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	196,766	113,778
Commercial and industrial | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	102,667	112,786
Commercial real estate — owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans	900,913	802,209
Commercial real estate — owner occupied | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	830,489	723,291
Commercial real estate — owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	15,378	14,181
Commercial real estate — owner occupied | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	34,410	41,997
Commercial real estate — owner occupied | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	20,636	22,740
Commercial and business lending
Financing Receivable, Recorded Investment [Line Items]
Loans	7,657,896	7,201,902
Commercial and business lending | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	7,155,747	6,739,175
Commercial and business lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	147,670	171,426
Commercial and business lending | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	231,176	155,775
Commercial and business lending | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	123,303	135,526
Commercial real estate — investor
Financing Receivable, Recorded Investment [Line Items]
Loans	4,077,671	3,315,254
Commercial real estate — investor | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	3,960,155	3,266,389
Commercial real estate — investor | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	54,972	24,845
Commercial real estate — investor | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	46,970	19,291
Commercial real estate — investor | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	15,574	4,729
Real estate construction
Financing Receivable, Recorded Investment [Line Items]
Loans	1,579,778	1,451,684
Real estate construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	1,547,443	1,421,504
Real estate construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	29,421	29,206
Real estate construction | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	1,695	0
Real estate construction | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	1,219	974
Commercial real estate lending
Financing Receivable, Recorded Investment [Line Items]
Loans	5,657,449	4,766,938
Commercial real estate lending | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	5,507,598	4,687,893
Commercial real estate lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	84,393	54,051
Commercial real estate lending | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	48,665	19,291
Commercial real estate lending | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	16,793	5,703
Total commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	13,315,345	11,968,840
Total commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	12,663,345	11,427,068
Total commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	232,063	225,477
Total commercial | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	279,841	175,066
Total commercial | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	140,096	141,229
Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans	8,197,223	7,546,534
Residential mortgage | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	8,134,387	7,490,860
Residential mortgage | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	5,580	426
Residential mortgage | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	2,155	1,616
Residential mortgage | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	55,100	53,632
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	923,470	883,804
Home equity | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	908,682	868,958
Home equity | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	1,383	1,137
Home equity | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	188	195
Home equity | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	13,218	13,514
Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	374,453	385,813
Other consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	373,714	384,990
Other consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	600	652
Other consumer | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Other consumer | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	139	171
Total consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	9,495,146	8,816,151
Total consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	9,416,783	8,744,808
Total consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	7,563	2,215
Total consumer | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	2,343	1,811
Total consumer | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 68,456	$ 67,317