Fair Value Measurements - Fair Value Inputs, Quantitative Information (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Material write downs	$ 0.1	$ 0.2	$ 0.1	$ 0.7
Significant Unobservable Inputs (Level 3) | Carrying Amount | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Collateral dependent loans*	16.0		16.0		$ 41.3
Significant Unobservable Inputs (Level 3) | Estimated Fair Value | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Collateral dependent loans*	11.4		11.4		27.6
Collateral dependent loans | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Collateral dependent loans*					27.6
Collateral dependent loans | Significant Unobservable Inputs (Level 3) | Estimated Fair Value | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Collateral dependent loans*	$ 11.4		$ 11.4		27.6
Collateral dependent loans | Discount Rate | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis | Minimum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate	0		0
Collateral dependent loans | Discount Rate | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis | Maximum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate	0.56		0.56
Collateral dependent loans | Discount Rate | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis | Weighted Average | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate	0.22		0.22
Other real estate owned | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other real estate owned	$ 1.1		$ 1.1		2.2
Other real estate owned | Significant Unobservable Inputs (Level 3) | Estimated Fair Value | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other real estate owned	$ 1.1		$ 1.1		2.2
Other real estate owned | Discount Rate | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis | Minimum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate	0.08		0.08
Other real estate owned | Discount Rate | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis | Maximum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate	0.65		0.65
Other real estate owned | Discount Rate | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis | Weighted Average | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate	0.27		0.27
Long-lived assets to be disposed of by sale | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Long-lived assets to be disposed of by sale	$ 5.0		$ 5.0		6.2
Long-lived assets to be disposed of by sale | Significant Unobservable Inputs (Level 3) | Estimated Fair Value | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Long-lived assets to be disposed of by sale	$ 5.0		$ 5.0		$ 6.2
Long-lived assets to be disposed of by sale | Discount Rate | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis | Minimum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate	0		0
Long-lived assets to be disposed of by sale | Discount Rate | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis | Maximum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate	0.37		0.37
Long-lived assets to be disposed of by sale | Discount Rate | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis | Weighted Average | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate	0.03		0.03