Subsequent Events (Details) (USD $)	3 Months Ended		0 Months Ended	1 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	May 01, 2015	May 08, 2015	May 10, 2015
Subsequent events
Gross proceeds from sale of common stock by the entity (in dollars)	$ 5,558,000	$ 22,606,000
Selling agent fees	153,000
June 2012 Amended Controlled Equity Offering Sales Agreement
Subsequent events
Common stock sold by the entity (in shares)	1,342,298
Gross proceeds from sale of common stock by the entity (in dollars)	5,600,000
Common stock price (in dollars per share)	$ 4.14
Selling agent fees	150,000
Subsequent Event | Convertible Senior Notes Due 2019
Subsequent events
Semiannual interest payment			7,400,000
Subsequent Event | June 2012 Amended Controlled Equity Offering Sales Agreement
Subsequent events
Common stock sold by the entity (in shares)				2,093,700
Gross proceeds from sale of common stock by the entity (in dollars)				9,100,000
Common stock price (in dollars per share)				$ 4.35
Selling agent fees				250,000.0000
Common stock, available unsold under agreement (in dollars)					$ 25,800,000