Summary of Significant Accounting Policies New Accounting Pronouncements - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) Segment	Jan. 01, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of portfolio segments | Segment	2
ROU lease assets				$ 127,481	$ 157,234
Lease liabilities	$ 158,280		$ 174,396	$ 158,280	$ 178,802
Allowance for credit losses on investment securities held-to-maturity	(299)		0
Financing Receivable, Allowance for Credit Loss			(209,096)
Deferred Tax Assets, Tax Deferred Expense			61,975
Accrued expenses and other liabilities	166,167		153,161
Retained earnings	2,077,522		2,061,352
Individually evaluated for impairment	16,137		14,249			$ 15,350
Collectively evaluated for impairment	$ 343,294		$ 194,847			$ 197,003
Building and Building Improvements | Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Building and Building Improvements | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Leasehold Improvements | Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Leasehold Improvements | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Furniture and Fixtures | Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Furniture and Fixtures | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Information Technology and Data Processing | Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Information Technology and Data Processing | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, Plant and Equipment, Useful Life	7 years
Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on investment securities held-to-maturity	$ (397)	$ (397)
Financing Receivable, Allowance for Credit Loss	(57,568)	(266,664)
Deferred Tax Assets, Tax Deferred Expense	15,891	77,866
Accrued expenses and other liabilities	9,139	162,300
Retained earnings	$ (51,213)	2,010,139
Individually evaluated for impairment		(14,200)
Collectively evaluated for impairment		$ (252,500)