Subsequent Events (Details) - USD ($)	1 Months Ended		3 Months Ended	6 Months Ended
	Aug. 10, 2015	Jun. 30, 2015	Jun. 30, 2015	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2015	Dec. 31, 2014	Nov. 03, 2014	Nov. 01, 2014
Subsequent events
Debt conversion amount				$ 22,213,000
Proceeds from exercise of stock options					$ 36,000
Convertible Senior Notes Due 2019
Subsequent events
Debt conversion amount		$ 22,200,000	$ 22,213,000	$ 22,200,000
Number of shares issued on conversion of debt		7,100,000		7,100,000
Aggregate principal amount (in dollars)		$ 177,787,000	$ 177,787,000	$ 177,787,000		$ 200,000,000	$ 200,000,000	$ 200,000,000	$ 200,000,000
Subsequent Event | Convertible Senior Notes Due 2019
Subsequent events
Debt conversion amount	$ 16,000,000
Number of shares issued on conversion of debt	5,000,000
Aggregate principal amount (in dollars)	$ 162,000,000
Subsequent Event | Warrants
Subsequent events
Number of shares purchased in exercise of warrants	189,412
Proceeds from exercise of warrants	$ 1,011,343
Subsequent Event | Employee Stock Option
Subsequent events
Number of shares purchased in exercise of options	62,965
Proceeds from exercise of stock options	$ 353,234