Debt - Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Jan. 31, 2017	Dec. 31, 2016
Long-term debt
Other	$ 181		$ 297
Long-term Debt	4,055,944		3,604,681
Less: current portion	181		297
Less: deferred financing costs	27,997		26,049
Long-term Debt, Excluding Current Maturities, Total	4,027,766		3,578,335
Maturity of primary debt
2018	460,837
2019	303,489
2020	1,220,675
2021	696,000
Thereafter	1,522,300
Total	$ 4,203,301
2.35% senior notes due September 2016
Long-term debt
Interest rate on senior notes due (as a percent)	2.35%
6.15% senior notes due February 2018
Long-term debt
Senior Notes	$ 460,762		827,539
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		303,489
Interest rate on senior notes due (as a percent)	9.25%
5.00% senior notes due September 2020
Long-term debt
Senior Notes	$ 669,846		669,540
Interest rate on senior notes due (as a percent)	5.00%
4.625% senior notes due September 2021
Long-term debt
Senior Notes	$ 695,108		694,868
Interest rate on senior notes due (as a percent)	4.625%
5.10% senior notes due September 2023
Long-term debt
Senior Notes	$ 346,576		346,448
Interest rate on senior notes due (as a percent)	5.10%
5.50% senior notes due January 2023
Long-term debt
Senior Notes	$ 600,000		600,000
Interest rate on senior notes due (as a percent)	5.50%
0.75% senior exchangeable notes due January 2024
Long-term debt
Senior Notes	$ 429,982
Less: deferred financing costs		$ 9,600
Interest rate on senior notes due (as a percent)	0.75%	0.75%
Term Loan Facility
Long-term debt
Senior Notes			$ 162,500
Revolving Credit Facility
Long-term debt
Revolving credit facility	$ 510,000
Commercial paper
Long-term debt
Revolving credit facility	40,000
Long-term Debt	$ 40,000