Loans, Credit Quality Indicator by Quality Indicator (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 24,451,724	$ 22,821,440
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		22,294,939
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		247,022
Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans		161,097
Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		118,380
Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans	7,701,422	7,354,594
Commercial and industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		7,118,448
Commercial and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		79,525
Commercial and industrial | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans		110,308
Commercial and industrial | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		46,312
Commercial real estate - owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans	900,912	911,265
Commercial real estate - owner occupied | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		866,193
Commercial real estate - owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		25,115
Commercial real estate - owner occupied | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans		19,889
Commercial real estate - owner occupied | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		67
Commercial and business lending
Financing Receivable, Recorded Investment [Line Items]
Loans	9,370,091	8,265,858
Commercial and business lending | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		7,984,641
Commercial and business lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		104,641
Commercial and business lending | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans		130,197
Commercial and business lending | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		46,380
Commercial real estate - investor
Financing Receivable, Recorded Investment [Line Items]
Loans	4,342,584	3,794,517
Commercial real estate - investor | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		3,620,785
Commercial real estate - investor | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		139,873
Commercial real estate - investor | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans		29,449
Commercial real estate - investor | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		4,409
Real estate construction
Financing Receivable, Recorded Investment [Line Items]
Loans	1,840,417	1,420,900
Real estate construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		1,420,374
Real estate construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		33
Real estate construction | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Real estate construction | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		493
Commercial real estate lending
Financing Receivable, Recorded Investment [Line Items]
Loans	6,183,001	5,215,417
Commercial real estate lending | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		5,041,159
Commercial real estate lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		139,906
Commercial real estate lending | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans		29,449
Commercial real estate lending | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		4,902
Total commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	15,553,091	13,481,275
Total commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		13,025,800
Total commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		244,547
Total commercial | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans		159,646
Total commercial | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		51,282
Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans	7,878,324	8,136,980
Residential mortgage | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		8,077,122
Residential mortgage | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		563
Residential mortgage | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans		1,451
Residential mortgage | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		57,844
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	707,255	852,025
Home equity | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		841,757
Home equity | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		1,164
Home equity | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Home equity | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		9,104
Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	313,054	351,159
Other consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		350,260
Other consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		748
Other consumer | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other consumer | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		152
Total consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 8,898,632	9,340,164
Total consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		9,269,139
Total consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		2,475
Total consumer | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans		1,451
Total consumer | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		$ 67,099