Subsequent Events (Details) (USD $)	9 Months Ended			0 Months Ended		1 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 June 2012 Amended Controlled Equity Offering Sales Agreement	Nov. 03, 2014 Subsequent Event Convertible Senior Notes Due 2019	Nov. 03, 2014 Subsequent Event Convertible Senior Notes Due 2019	Oct. 24, 2014 Subsequent Event June 2012 Amended Controlled Equity Offering Sales Agreement	Nov. 10, 2014 Subsequent Event June 2012 Amended Controlled Equity Offering Sales Agreement
Subsequent events
Common stock sold by the entity (in shares)			4,604,130			1,813,520
Gross proceeds from sale of common stock by the entity (in dollars)	$ 25,612,000	$ 94,734,000	$ 25,600,000			$ 5,100,000
Common stock, average selling price (in dollars per share)			$ 5.56			$ 2.81
Common stock, available unsold under agreement (in dollars)							41,000,000
Aggregate principal amount (in dollars)					200,000,000
Interest rate (as a percent)					7.50%
Additional aggregate principal amount pertaining to the over-allotment option granted (in dollars)					25,000,000
Repurchase price (as a percent)				100.00%
Conversion rate (as a percent)				0.3215434
Conversion price (in dollars per share)					$ 3.11
Net proceeds from offering (in dollars)				$ 187,300,000