Debt (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 2.35% senior notes due September 2016	Sep. 30, 2013 2.35% senior notes due September 2016	Dec. 31, 2013 6.15% senior notes due February 2018	Dec. 31, 2012 6.15% senior notes due February 2018	Dec. 31, 2013 9.25% senior notes due January 2019	Dec. 31, 2012 9.25% senior notes due January 2019	Dec. 31, 2013 5.00% senior notes due September 2020	Dec. 31, 2012 5.00% senior notes due September 2020	Dec. 31, 2013 4.625% senior notes due September 2021	Dec. 31, 2012 4.625% senior notes due September 2021
Debt
Interest rate on senior note due (as a percent)			2.35%	2.35%	6.15%		9.25%		5.00%		4.625%
Maturity of primary debt
2016	$ 350,000
2017	499,844
2018	975,000
Thereafter	2,089,607
Long-term debt total	$ 3,983,490	$ 4,448,888	$ 349,820		$ 969,928	$ 968,708	$ 339,607	$ 1,125,000	$ 697,947	$ 697,648	$ 698,148	$ 697,907