Supplemental Guarantor Information (Details)	6 Months Ended
	Jun. 30, 2014
Interest rate on obligations of the parent, guaranteed by the Guarantor Subsidiaries
Ownership interest in subsidiaries (as a percent)	100.00%
5.4 percent senior notes due January 2015
Interest rate on obligations of the parent, guaranteed by the Guarantor Subsidiaries
Interest rate stated percentage	5.40%
8.4 percent senior notes due May 2017
Interest rate on obligations of the parent, guaranteed by the Guarantor Subsidiaries
Interest rate stated percentage	8.40%
1.6 percent convertible senior notes due May 2018
Interest rate on obligations of the parent, guaranteed by the Guarantor Subsidiaries
Interest rate stated percentage	1.60%
0.25 percent convertible senior notes due June 2019
Interest rate on obligations of the parent, guaranteed by the Guarantor Subsidiaries
Interest rate stated percentage	0.25%
6.6 percent senior notes due May 2020
Interest rate on obligations of the parent, guaranteed by the Guarantor Subsidiaries
Interest rate stated percentage	6.60%
5.4 percent senior notes due October 2022
Interest rate on obligations of the parent, guaranteed by the Guarantor Subsidiaries
Interest rate stated percentage	5.40%