Loans Credit Quality Indicator (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 23,148,359	$ 22,940,429
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	22,662,534	22,438,605
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	88,912	123,988
Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	241,357	249,935
Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	155,556	127,901
Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans	7,587,597	7,398,044
Commercial and industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	7,371,790	7,162,370
Commercial and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	30,657	78,075
Commercial and industrial | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	111,772	116,578
Commercial and industrial | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	73,379	41,021
Commercial real estate — owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans	932,393	920,443
Commercial real estate — owner occupied | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	874,152	854,265
Commercial real estate — owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	8,422	6,257
Commercial real estate — owner occupied | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	48,929	55,964
Commercial real estate — owner occupied | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	890	3,957
Commercial and business lending
Financing Receivable, Recorded Investment [Line Items]
Loans	8,519,990	8,318,487
Commercial and business lending | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	8,245,942	8,016,635
Commercial and business lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	39,079	84,332
Commercial and business lending | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	160,701	172,542
Commercial and business lending | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	74,269	44,978
Commercial real estate — investor
Financing Receivable, Recorded Investment [Line Items]
Loans	3,809,253	3,751,554
Commercial real estate — investor | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	3,698,679	3,653,642
Commercial real estate — investor | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	39,184	28,479
Commercial real estate — investor | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	70,613	67,481
Commercial real estate — investor | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	776	1,952
Real estate construction
Financing Receivable, Recorded Investment [Line Items]
Loans	1,273,782	1,335,031
Real estate construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	1,259,661	1,321,447
Real estate construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	8,782	8,771
Real estate construction | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	4,600	3,834
Real estate construction | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	739	979
Commercial real estate lending
Financing Receivable, Recorded Investment [Line Items]
Loans	5,083,035	5,086,585
Commercial real estate lending | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	4,958,341	4,975,089
Commercial real estate lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	47,966	37,249
Commercial real estate lending | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	75,213	71,315
Commercial real estate lending | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	1,516	2,931
Total commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	13,603,025	13,405,072
Total commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	13,204,282	12,991,724
Total commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	87,045	121,582
Total commercial | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	235,914	243,856
Total commercial | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	75,784	47,909
Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans	8,323,846	8,277,712
Residential mortgage | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	8,250,915	8,203,729
Residential mortgage | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	256	434
Residential mortgage | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	5,351	5,975
Residential mortgage | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	67,323	67,574
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	868,886	894,473
Home equity | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	855,603	880,808
Home equity | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	891	1,223
Home equity | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	91	103
Home equity | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	12,300	12,339
Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	352,602	363,171
Other consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	351,734	362,343
Other consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	719	749
Other consumer | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Other consumer | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	149	79
Total consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	9,545,333	9,535,357
Total consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	9,458,252	9,446,881
Total consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	1,866	2,406
Total consumer | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	5,443	6,078
Total consumer | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 79,772	$ 79,992