Stockholders' Equity (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Stockholders' Equity
Increase in total stockholders' equity	$ 18,700,000
Increase in total stockholders' equity allocated to equity portion of Convertible Notes	38,188,000
Increase in total stockholders' equity allocated to stock-based compensation expense	1,930,000	2,283,000
Increase in total stockholders' equity partially offset by net loss	7,102,000	3,895,000
Increase in total stockholders' equity partially offset by paying for the cost of the convertible bond hedges, net of the sale of warrants	14,100,000
Increase in total stockholders' equity partially offset by debt issuance costs allocated to equity component of the Convertible Notes	$ 1,300,000