Debt (Details)		1 Months Ended	3 Months Ended
	Sep. 29, 2015 USD ($)	Jan. 31, 2017 USD ($) $ / shares	Mar. 31, 2017 USD ($) $ / shares	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Long-term debt
Senior Notes			$ 600,000,000		$ 600,000,000
Other			313,000		297,000
Less: current portion			313,000		297,000
Less: deferred financing costs			33,298,000		26,049,000
Long-term Debt, Excluding Current Maturities, Total			3,661,665,000		3,578,335,000
Reduction in long-term debt			170,491,000	$ 148,045,000
Senior Notes.
Long-term debt
Reduction in long-term debt			171,600,000
Payment of debt accrued interest			2,200,000
Consolidated affiliate | Senior Notes.
Long-term debt
Principal amount redeemed			162,500,000
6.15% senior notes due February 2018
Long-term debt
Senior Notes			$ 665,222,000		827,539,000
Interest rate on senior notes due (as a percent)			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			$ 669,616,000		669,540,000
Interest rate on senior notes due (as a percent)			5.00%
4.625% senior notes due September 2021
Long-term debt
Senior Notes			$ 694,928,000		694,868,000
Interest rate on senior notes due (as a percent)			4.625%
5.50% senior notes due January 2023
Long-term debt
Interest rate on senior notes due (as a percent)			5.50%
5.10% senior notes due September 2023
Long-term debt
Senior Notes			$ 346,480,000		346,448,000
Interest rate on senior notes due (as a percent)			5.10%
0.75% senior exchangeable notes due January 2024
Long-term debt
Senior Notes			$ 415,228,000
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		$ 1,000,000
Share issued price | $ / shares		$ 25.16	$ 25.16
Share price of shares purchased (in dollars per share) | $ / shares		$ 17.97	$ 31.45
Premium over share price (as a percent)			75.00%
Prepayment of loan upon closing the merger		$ 162,500,000
Term Loan Facility
Long-term debt
Senior Notes					162,500,000
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
Remaining availability under credit facility			$ 2,250,000,000
Debt to capital ratio			0.60
Commercial paper
Long-term debt
Long-term Debt			$ 3,695,276,000		$ 3,604,681,000
Commercial paper | Minimum
Long-term debt
Remaining period to maturity			1 year