Fair Value Measurements and Disclosures Notes Receivable (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
1.125% Convertible Senior Notes due 2021 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes Payable, Fair Value Disclosure	$ 188.1	$ 175.4
Senior Notes fair value	94.10%	87.70%
5.75% Senior Notes due 2026 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes Payable, Fair Value Disclosure	$ 583.7	$ 532.4
Senior Notes fair value	97.30%	88.70%
6.125% Senior Notes due 2024 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes Payable, Fair Value Disclosure	$ 398.9	$ 370.2
Senior Notes fair value	99.70%	92.50%