Loans Credit Quality Indicator (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 22,754,710	$ 22,940,429
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	22,240,647	22,438,605
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	251,934	123,988
Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	133,189	249,935
Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	128,939	127,901
Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	7,495,623	7,398,044
Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	7,293,226	7,162,370
Commercial and industrial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	86,434	78,075
Commercial and industrial | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	59,427	116,578
Commercial and industrial | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	56,536	41,021
Commercial real estate — owner occupied
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	915,524	920,443
Commercial real estate — owner occupied | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	866,287	854,265
Commercial real estate — owner occupied | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	26,546	6,257
Commercial real estate — owner occupied | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	22,624	55,964
Commercial real estate — owner occupied | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	68	3,957
Commercial and business lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	8,411,147	8,318,487
Commercial and business lending | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	8,159,513	8,016,635
Commercial and business lending | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	112,980	84,332
Commercial and business lending | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	82,051	172,542
Commercial and business lending | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	56,604	44,978
Commercial real estate — investor
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,803,277	3,751,554
Commercial real estate — investor | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,634,780	3,653,642
Commercial real estate — investor | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	114,343	28,479
Commercial real estate — investor | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	49,353	67,481
Commercial real estate — investor | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	4,800	1,952
Real estate construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,356,508	1,335,031
Real estate construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,332,930	1,321,447
Real estate construction | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	22,492	8,771
Real estate construction | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	544	3,834
Real estate construction | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	542	979
Commercial real estate lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	5,159,784	5,086,585
Commercial real estate lending | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	4,967,710	4,975,089
Commercial real estate lending | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	136,835	37,249
Commercial real estate lending | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	49,897	71,315
Commercial real estate lending | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	5,342	2,931
Total commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	13,570,932	13,405,072
Total commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	13,127,223	12,991,724
Total commercial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	249,815	121,582
Total commercial | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	131,948	243,856
Total commercial | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	61,946	47,909
Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 7,954,801	8,277,712
Approximate Carrying Amount of Loans Sold	approximately $240 million
Residential mortgage | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 7,896,073	8,203,729
Residential mortgage | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	430	434
Residential mortgage | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,242	5,975
Residential mortgage | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	57,056	67,574
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	879,642	894,473
Home equity | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	868,854	880,808
Home equity | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	961	1,223
Home equity | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	103
Home equity | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	9,828	12,339
Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	349,335	363,171
Other consumer | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	348,498	362,343
Other consumer | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	728	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	109	79
Total consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	9,183,778	9,535,357
Carrying Amount Of Loans Sold	33,000
Total consumer | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	9,113,424	9,446,881
Total consumer | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,119	2,406
Total consumer | Potential Problem
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,242	6,078
Total consumer | Nonaccrual
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	66,993	$ 79,992
Carrying Amount Of Loans Sold	$ 12,000