Nature of Operations (Details 2) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) item
Nature Of Operation
Increase in restricted cash related to sale/leaseback transactions	$ 29.7
Gross proceeds from shares of common stock sold in an underwritten public offering		$ 176.7	$ 176.7
Number of underwritten public offerings | item			3
Net proceeds from public offering		165.7	$ 165.7
Net proceeds from previously issued common stock warrants		$ 18.3	$ 18.3
Minimum period for which we believe that our current cash, cash equivalents, cash generated from future sales, and cash generated from the exercise of outstanding warrants will provide sufficient liquidity to fund operations	12 months