Debt (Details)		1 Months Ended	3 Months Ended
	Sep. 29, 2015 USD ($)	Jan. 31, 2017 USD ($) $ / shares	Mar. 31, 2018 USD ($) $ / shares	Mar. 31, 2017 USD ($)	Feb. 28, 2018	Jan. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Long-term debt
Other			$ 375,000				$ 181,000
Long-term Debt			4,295,636,000				4,055,944,000
Less: current portion			375,000				181,000
Less: deferred financing costs			39,101,000				27,997,000
Long-term Debt, Excluding Current Maturities, Total			4,256,160,000				4,027,766,000
Reduction in long-term debt			460,837,000	$ 170,491,000
Senior Notes.
Long-term debt
Principal amount redeemed			460,800,000
Reduction in long-term debt			475,000,000
Payment of debt accrued interest			$ 14,200,000
6.15% senior notes due February 2018
Long-term debt
Senior Notes							$ 460,762,000
Interest rate on senior notes due (as a percent)			6.15%		6.15%		6.15%
9.25% senior notes due January 2019
Long-term debt
Senior Notes			$ 303,489,000				$ 303,489,000
Interest rate on senior notes due (as a percent)			9.25%
5.00% senior notes due September 2020
Long-term debt
Senior Notes			$ 669,922,000				669,846,000
Interest rate on senior notes due (as a percent)			5.00%
4.625% senior notes due September 2021
Long-term debt
Senior Notes			$ 695,168,000				695,108,000
Interest rate on senior notes due (as a percent)			4.625%
5.50% senior notes due January 2023
Long-term debt
Senior Notes			$ 600,000,000				600,000,000
Interest rate on senior notes due (as a percent)			5.50%
5.10% senior notes due September 2023
Long-term debt
Senior Notes			$ 346,608,000				346,576,000
Interest rate on senior notes due (as a percent)			5.10%
0.75% senior exchangeable notes due January 2024
Long-term debt
Senior Notes			$ 435,074,000				429,982,000
Less: deferred financing costs		$ 9,600,000
Interest rate on senior notes due (as a percent)			0.75%
Aggregate amount of senior notes		575,000,000	$ 575,000,000
Debt exchangeable notes			$ 411,200,000
Equity component				$ 163,800,000
Equity issuance costs		$ 3,900,000
Exchange rate of common shares		39.75
Principal amount of notes		$ 1,000
Exchange price per common share (in dollars per share) | $ / shares		$ 25.16
Premium over share price (as a percent)			75.00%
Share price of shares purchased (in dollars per share) | $ / shares		$ 17.97
Prepayment of loan upon closing the merger		$ 162,500,000
0.75% senior exchangeable notes due January 2024 | Maximum
Long-term debt
Exchange price per common share (in dollars per share) | $ / shares			$ 31.45
5.75% senior notes due February 2025
Long-term debt
Senior Notes			$ 800,000,000
Interest rate on senior notes due (as a percent)			5.75%
Aggregate amount of senior notes						$ 800,000,000
Five-year term loan facility
Long-term debt
Maximum borrowing capacity	$ 325,000,000
Unsecured debt maturity period	5 years
Prepayment of loan upon closing the merger	$ 162,500,000
Revolving Credit Facility
Long-term debt
Revolving credit facility			$ 445,000,000				510,000,000
Amount outstanding			445,000,000
Maximum borrowing capacity			$ 2,250,000,000
Weighted average interest rate (as a percent)			3.15%
Debt to capital ratio			0.60
Commercial paper
Long-term debt
Revolving credit facility			$ 0
Long-term Debt							$ 40,000,000
Commercial paper | Minimum
Long-term debt
Remaining period to maturity			1 year
Guarantor Subsidiaries
Long-term debt
Redemption price of principal amount of debt instrument including accrued and unpaid interest (as a percent)			101.00%