Fair Value Measurements and Risk - Carrying Amounts and Fair Values of Debt (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Sep. 16, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, Long-term and Short-term, Combined Amount	$ 1,980.4	$ 1,983.3
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, Long-term and Short-term, Combined Amount	1,980.4	1,983.3
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, Long-term and Short-term, Combined Amount	2,049.0	1,965.7
2018 Credit Agreement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	7.2	8.7
2018 Credit Agreement [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, Long-term and Short-term, Combined Amount	930.9	938.9
2018 Credit Agreement [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, Long-term and Short-term, Combined Amount	938.1	914.8
Senior Notes, Due 2021 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, Long-term and Short-term, Combined Amount	697.3	695.8
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	$ 2.7	$ 4.2
Debt Instrument, Interest Rate, Stated Percentage	5.125%	5.125%	5.125%
Senior Notes, Due 2021 [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, Long-term and Short-term, Combined Amount	$ 697.3	$ 695.8
Senior Notes, Due 2021 [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, Long-term and Short-term, Combined Amount	727.1	697.5
Senior Notes, Due 2024 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, Long-term and Short-term, Combined Amount	297.6	297.0
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	$ 2.4	$ 3.0
Debt Instrument, Interest Rate, Stated Percentage	5.625%	5.625%	5.625%
Senior Notes, Due 2024 [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, Long-term and Short-term, Combined Amount	$ 297.6	$ 297.0
Senior Notes, Due 2024 [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, Long-term and Short-term, Combined Amount	329.2	301.8
Other borrowings [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, Long-term and Short-term, Combined Amount	54.6	51.6
Other borrowings [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, Long-term and Short-term, Combined Amount	$ 54.6	$ 51.6