Stockholders' Equity (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Stockholders' Equity
Increase in total stockholders' equity			$ 20,600,000
Increase in total stockholders' equity allocated to equity portion of Convertible Notes	38,188,000		38,188,000
Increase in total stockholders' equity allocated to stock-based compensation expense			4,207,000	4,221,000
Increase in total stockholders' equity due to proceeds from exercise of stock options			2,021,000	379,000
Increase in total stockholders' equity partially offset by net loss	1,547,000	1,908,000	8,649,000	5,803,000
Increase in total stockholders' equity partially offset by 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