Fair Value Measurements and Disclosures of Senior Notes (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impairment Measurement Input	17.00%
1.125% Convertible Senior Notes due 2021 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes Payable, Fair Value Disclosure	$ 192.6	$ 188.6
Senior Notes Percent of Par	96.30%	94.30%
6.125% Senior Notes due 2024 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes Payable, Fair Value Disclosure	$ 382.8	$ 409.2
Senior Notes Percent of Par	95.70%	102.30%
6.25% Senior Notes due 2025 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes Payable, Fair Value Disclosure	$ 96.1	$ 0.0
Senior Notes Percent of Par	93.90%	0.00%
5.75% Senior Notes due 2026 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes Payable, Fair Value Disclosure	$ 696.8	$ 599.4
Senior Notes Percent of Par	92.90%	99.90%