Fair Value Measurements - Fair Value Inputs, Quantitative Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Minimum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount Rate for Level 3 Fair Value Disclosure	(0.00%)	(0.00%)
Maximum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount Rate for OREO Level 3 Fair Value	(96.00%)	(96.00%)
Discount Rate for Assets HFS Level 3 Fair Value	43.00%	0.00%
Weighted Average | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount Rate for Level 3 Fair Value Disclosure	(13.00%)	(26.00%)
Discount Rate for OREO Level 3 Fair Value	(39.00%)	(12.00%)
Discount Rate for Assets HFS Level 3 Fair Value	10.00%	0.00%
Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Impaired loans	$ (12.2)	$ (22.2)
Other real estate owned	(0.6)	(1.6)
Long-lived assets to be disposed of by sale	(0.5)	0.0
Estimated Fair Value | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Impaired loans	24.1
Other real estate owned	0.6
Long-lived assets to be disposed of by sale	4.9
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Impaired loans	0.0	0.0
Other real estate owned	0.0	0.0
Long-lived assets to be disposed of by sale	0.0	0.0
Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Impaired loans	0.0	0.0
Other real estate owned	0.0	0.0
Long-lived assets to be disposed of by sale	0.0	0.0
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)
Impaired loans	24.1	32.6
Other real estate owned	0.6	1.3
Long-lived assets to be disposed of by sale	4.9	0.8
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)
Impaired loans	$ 24.1	$ 32.6
Measurement Input, Discount Rate [Member] | Minimum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount Rate for OREO Level 3 Fair Value	(8.00%)	(8.00%)
Discount Rate for Assets HFS Level 3 Fair Value	0.00%	0.00%
Measurement Input, Discount Rate [Member] | Maximum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount Rate for Level 3 Fair Value Disclosure	(26.00%)	(78.00%)