Summary of Significant Accounting Policies - Impact of Adoption (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt securities held to maturity, allowance for credit losses	$ 40
Allowance for credit loss	363,000	$ 196,000	$ 196,000	$ 180,000	$ 175,000
Allowance for credit losses on off-balance sheet credit exposures		3,000
As Reported Under ASC 326
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		301,000
Allowance for credit losses on off-balance sheet credit exposures		13,000
Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		105,000
Allowance for credit losses on off-balance sheet credit exposures		10,000
States of the U.S. and political subdivisions (municipals)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt securities held to maturity, allowance for credit losses	40	0
States of the U.S. and political subdivisions (municipals) | As Reported Under ASC 326
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt securities held to maturity, allowance for credit losses		0
States of the U.S. and political subdivisions (municipals) | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt securities held to maturity, allowance for credit losses		0
Commercial real estate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss	181,000	60,000	60,000
Commercial real estate | As Reported Under ASC 326
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		138,000
Commercial real estate | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		78,000
Commercial and industrial
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss	81,000	53,000	53,000
Commercial and industrial | As Reported Under ASC 326
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		65,000
Commercial and industrial | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		12,000
Commercial leases
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss	17,000	11,000	11,000
Commercial leases | As Reported Under ASC 326
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		11,000
Commercial leases | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		0
Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss	1,000	9,000	9,000
Other | As Reported Under ASC 326
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		0
Other | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		(9,000)
Direct installment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss	26,000	13,000	13,000
Direct installment | As Reported Under ASC 326
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		24,000
Direct installment | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		11,000
Residential mortgages
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss	34,000	22,000	22,000
Residential mortgages | As Reported Under ASC 326
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		32,000
Residential mortgages | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		10,000
Indirect installment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss	11,000	19,000	19,000
Indirect installment | As Reported Under ASC 326
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		21,000
Indirect installment | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		2,000
Consumer lines of credit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss	$ 12,000	9,000	$ 9,000
Consumer lines of credit | As Reported Under ASC 326
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		10,000
Consumer lines of credit | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss		$ 1,000