Convertible Notes (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Interest expense related to notes
Amortization of discount and debt issuance costs	$ 6,242	$ 4,089
Interest expense	9,926	7,312
Convertible Senior Notes [Member]
Interest expense related to notes
Interest expense	8,786	6,246
Convertible Senior Notes [Member] | 5% Convertible Senior Notes due 2014
Debt Instrument [Line Items]
Additional Effective Interest Rate	11.70%	11.70%
Interest expense related to notes
Interest	2,156	2,157
Amortization of discount and debt issuance costs	4,769	4,089
Convertible notes stated interest rate (as a percent)	5.00%		5.00%
Convertible Senior Notes [Member] | 1.125% Convertible Senior Notes due 2018
Debt Instrument [Line Items]
Additional Effective Interest Rate	5.50%	5.50%
Interest expense related to notes
Interest	388	0
Amortization of discount and debt issuance costs	$ 1,473	$ 0
Convertible notes stated interest rate (as a percent)	1.125%		1.125%