Fair Value Measurements - Table 2 (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Revolving Credit Facility [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying amounts and estimated fair values of financial instruments	$ 65.0	$ 95.0
Revolving Credit Facility [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying amounts and estimated fair values of financial instruments	65.0	95.0
Letters of Credit [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying amounts and estimated fair values of financial instruments	0.0	0.0
Letters of Credit [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying amounts and estimated fair values of financial instruments	39.7	35.4
Term Loan Facilities [Member] | Term Loan Facilities [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying amounts and estimated fair values of financial instruments	283.7	294.7
Term Loan Facilities [Member] | Term Loan Facilities [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying amounts and estimated fair values of financial instruments	$ 285.0	$ 296.3
Senior Notes [Member] | 5.125% Senior Notes Due 2023 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument interest rate (percent)	5.125%	5.125%
Senior Notes [Member] | 5.125% Senior Notes Due 2023 [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying amounts and estimated fair values of financial instruments	$ 296.4	$ 295.9
Senior Notes [Member] | 5.125% Senior Notes Due 2023 [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying amounts and estimated fair values of financial instruments	$ 302.6	$ 306.8
Senior Notes [Member] | 5.75% Senior Notes Due 2024 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument interest rate (percent)	5.75%	5.75%
Senior Notes [Member] | 5.75% Senior Notes Due 2024 [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying amounts and estimated fair values of financial instruments	$ 1,194.5	$ 1,193.9
Senior Notes [Member] | 5.75% Senior Notes Due 2024 [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying amounts and estimated fair values of financial instruments	$ 1,216.4	$ 1,228.5
Senior Notes [Member] | 5.75% Senior Notes Due 2025 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument interest rate (percent)	5.75%	5.75%
Senior Notes [Member] | 5.75% Senior Notes Due 2025 [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying amounts and estimated fair values of financial instruments	$ 344.9	$ 344.4
Senior Notes [Member] | 5.75% Senior Notes Due 2025 [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying amounts and estimated fair values of financial instruments	354.9	364.9
Other Notes Payable [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying amounts and estimated fair values of financial instruments	92.0	82.3
Other Notes Payable [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying amounts and estimated fair values of financial instruments	$ 92.0	$ 82.3