Loans Credit Quality Indicator (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	[1]	$ 23,249,967	$ 22,940,429
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		22,777,758	22,438,605
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		139,660	123,988
Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		165,842	249,935
Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		166,707	127,901
Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		7,579,384	7,398,044
Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		7,387,549	7,162,370
Commercial and industrial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		49,026	78,075
Commercial and industrial | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		58,658	116,578
Commercial and industrial | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		84,151	41,021
Commercial real estate — owner occupied
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		942,811	920,443
Commercial real estate — owner occupied | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		909,641	854,265
Commercial real estate — owner occupied | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		8,362	6,257
Commercial real estate — owner occupied | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		24,237	55,964
Commercial real estate — owner occupied | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		571	3,957
Commercial and business lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		8,522,194	8,318,487
Commercial and business lending | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		8,297,189	8,016,635
Commercial and business lending | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		57,388	84,332
Commercial and business lending | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		82,895	172,542
Commercial and business lending | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		84,722	44,978
Commercial real estate — investor
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		3,779,201	3,751,554
Commercial real estate — investor | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		3,628,197	3,653,642
Commercial real estate — investor | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		71,753	28,479
Commercial real estate — investor | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		77,766	67,481
Commercial real estate — investor | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		1,485	1,952
Real estate construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		1,394,815	1,335,031
Real estate construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		1,382,502	1,321,447
Real estate construction | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		8,720	8,771
Real estate construction | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		3,166	3,834
Real estate construction | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		427	979
Commercial real estate lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		5,174,016	5,086,585
Commercial real estate lending | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		5,010,699	4,975,089
Commercial real estate lending | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		80,473	37,249
Commercial real estate lending | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		80,932	71,315
Commercial real estate lending | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		1,912	2,931
Total commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		13,696,210	13,405,072
Total commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		13,307,888	12,991,724
Total commercial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		137,860	121,582
Total commercial | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		163,828	243,856
Total commercial | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		86,634	47,909
Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		8,277,479	8,277,712
Residential mortgage | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		8,206,689	8,203,729
Residential mortgage | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		641	434
Residential mortgage | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		1,983	5,975
Residential mortgage | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		68,166	67,574
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		916,213	894,473
Home equity | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		903,694	880,808
Home equity | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		652	1,223
Home equity | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		32	103
Home equity | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		11,835	12,339
Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		360,065	363,171
Other consumer | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		359,487	362,343
Other consumer | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		506	749
Other consumer | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		0	0
Other consumer | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		72	79
Total consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		9,553,757	9,535,357
Total consumer | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		9,469,870	9,446,881
Total consumer | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		1,799	2,406
Total consumer | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		2,014	6,078
Total consumer | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans		$ 80,073	$ 79,992

[1] (a) Includes $2 million and $5 million of purchased credit-impaired loans at June 30, 2019 and December 31, 2018, respectively.