Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related allowance	$ 6.8	$ 10.8	$ 14.0
Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	(12.2)	(22.2)
Fair Value Measured on a Non-recurring Basis | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	24.1	32.6
Related allowance	6.8	10.8
Partial loan charge-off	5.4	11.4
Carrying Amount | Fair Value Measured on a Non-recurring Basis | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	36.3	54.8
Assets Held-for-sale, Long Lived, Fair Value Disclosure	5.4	0.8
Changes Measurement [Member] | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Held-for-sale, Long Lived, Fair Value Disclosure	0.5	0.0
Estimated Fair Value | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	24.1
Assets Held-for-sale, Long Lived, Fair Value Disclosure	4.9	0.8
Estimated Fair Value | Fair Value Measured on a Non-recurring Basis | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	$ 24.1	$ 32.6