Fair Value Measurements and Disclosures of Senior Notes (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
1.125% Convertible Senior Notes due 2021 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes Payable, Fair Value Disclosure	$ 198.2	$ 196.2
Senior Notes Percent of Par	99.10%	98.10%
6.125% Senior Notes due 2024 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes Payable, Fair Value Disclosure	$ 410.4	$ 410.8
Senior Notes Percent of Par	102.60%	102.70%
6.25% Senior Notes due 2025 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes Payable, Fair Value Disclosure	$ 102.8	$ 102.8
Senior Notes Percent of Par	100.50%	100.50%
5.75% Senior Notes due 2026 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes Payable, Fair Value Disclosure	$ 777.8	$ 775.5
Senior Notes Percent of Par	103.70%	103.40%