Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Details)		3 Months Ended	12 Months Ended
	Jan. 01, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) Unit
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Maximum refinement period of fair values after closing date of acquisition			1 year
Allowance for loan losses		$ 0	$ 0
Loan minimum balance included in specific reserve analysis			$ 1,000,000
Number of reporting units | Unit			1
Tax credit carry back period			1 year
Tax credit carry forward period			20 years
Operating Lease, Right-of-Use Asset		110,023,000	$ 110,023,000
Operating Lease, Liability		127,703,000	127,703,000
Reserve for unfunded lending commitments		3,974,000	3,974,000
Accounting Standards Update 2016-02 [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Operating Lease, Right-of-Use Asset		$ 116,300,000	$ 116,300,000
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]		us-gaap:Assets	us-gaap:Assets
Operating Lease, Liability		$ 131,100,000	$ 131,100,000
Operating Lease, Liability, Statement of Financial Position [Extensible List]		us-gaap:Liabilities	us-gaap:Liabilities
Deferred rent liabilities		$ 14,800,000	$ 14,800,000
Accounting Standards Update 2019-04 [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Transfer securities with amortized cost from its held to maturity portfolio to its available for sale portfolio		$ 1,200,000,000	$ 1,200,000,000
Accounting Standards Update 2016-13 [Member] | Subsequent Event [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Increase in allowance for credit losses	$ 76,700,000
Increases in ALLL	49,400,000
Reserve for unfunded lending commitments	27,300,000
Increase of ALLL reclassified from fair value mark for acquired impaired loans considered purchased credit deteriorated	19,800,000
Cumulative-effect adjustment to retained earnings(net of tax)	$ 44,100,000
Federal NMTC Investment [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Tax credit earning period			7 years
Low Income Housing Credit Investments [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Tax credit earning period			10 years
Buildings [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Estimated useful lives of assets			30 years
Software [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Amortization Expense Charged Off Period			3 years
Core Systems [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Amortization Expense Charged Off Period			7 years
Minimum [Member] | State NMTC Investment [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Tax credit earning period			3 years
Minimum [Member] | Furniture, Fixtures and Equipment [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Estimated useful lives of assets			3 years
Maximum [Member] | State NMTC Investment [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Tax credit earning period			5 years
Maximum [Member] | Furniture, Fixtures and Equipment [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Estimated useful lives of assets			10 years
Commercial Loans [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Loss emergence periods			24 months
Retail Loans [Member] | Minimum [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Loss emergence periods			12 months
Residential Mortgages Loans [Member] | Maximum [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Loss emergence periods			18 months