Allowance for Credit Losses - Collateral Dependent Loans by Class of Loan (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Jan. 01, 2020
Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	$ 62,638
Blanket Lien
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	5,421
Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	40
Other
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	689
Commercial | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans		$ 3,416,518
Commercial | Commercial real estate | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	51,630
Commercial | Commercial real estate | Blanket Lien
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	0
Commercial | Commercial real estate | Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	0
Commercial | Commercial real estate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	0
Commercial | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans		1,720,833
Commercial | Commercial and industrial | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	4,686
Commercial | Commercial and industrial | Blanket Lien
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	4,545
Commercial | Commercial and industrial | Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	40
Commercial | Commercial and industrial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	0
Commercial | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans		375,445
Commercial | Commercial construction | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	3,602
Commercial | Commercial construction | Blanket Lien
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	0
Commercial | Commercial construction | Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	0
Commercial | Commercial construction | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	0
Commercial | Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans		$ 0
Commercial | Business banking | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	2,322
Commercial | Business banking | Blanket Lien
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	876
Commercial | Business banking | Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	0
Commercial | Business banking | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	689
Commercial | Consumer real estate | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	0
Commercial | Consumer real estate | Blanket Lien
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	0
Commercial | Consumer real estate | Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	0
Commercial | Consumer real estate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	0
Commercial | Other consumer | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	398
Commercial | Other consumer | Blanket Lien
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	0
Commercial | Other consumer | Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	0
Commercial | Other consumer | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Collateral dependent loans	$ 0