Fair Value Measurements and Disclosures Notes Receivable (Details) $ in Millions	Mar. 31, 2018 USD ($)
1.125% Convertible Senior Notes due 2021 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes Payable, Fair Value Disclosure	$ 194.0
Senior Notes fair value	97.00%
5.75% Senior Notes due 2026 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes Payable, Fair Value Disclosure	$ 593.3
Senior Notes fair value	98.90%
6.125% Senior Notes due 2024 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes Payable, Fair Value Disclosure	$ 409.0
Senior Notes fair value	102.30%