Convertible Notes (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Interest expense related to notes
Amortization of discount and debt issuance costs			$ 11,711	$ 8,234
Interest expense	8,770	7,426	18,696	14,738
Convertible Senior Notes
Interest expense related to notes
Interest expense	7,630	6,301	16,416	12,547
Convertible Senior Notes | 5% Convertible Senior Notes due 2014
Interest expense related to notes
Interest	1,773	2,156	3,929	4,313
Amortization of discount and debt issuance costs	3,975	4,145	8,744	8,234
Convertible notes stated interest rate (as a percent)	5.00%	5.00%	5.00%	5.00%	5.00%
Additional Effective Interest Rate	11.70%	11.70%	11.70%	11.70%
Convertible Senior Notes | 1.125% Convertible Senior Notes due 2018
Interest expense related to notes
Interest	388	0	776	0
Amortization of discount and debt issuance costs	$ 1,494	$ 0	$ 2,967	$ 0
Convertible notes stated interest rate (as a percent)	1.125%	1.125%	1.125%	1.125%	1.125%
Additional Effective Interest Rate	5.50%	5.50%	5.50%	5.50%