Stockholders' Equity (Summary of Nonvested Options) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Options
Nonvested at beginning of period	4,592,187
Options granted	1,621,222
Options vested	(1,485,495)
Options forfeited	(9,880)
Nonvested at end of period	4,718,034
Weighted-Average Grant Date Fair Value
Nonvested at beginning of period (in dollars per share)	$ 3.61
Options granted (in dollars per share)	4.87	$ 3.37
Options vested (in dollars per share)	3.22
Options forfeited (in dollars per share)	4.51
Nonvested at end of period (in dollars per share)	$ 4.16
Employee Consultant And Directors Stock Options
Weighted-Average Grant Date Fair Value
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options	$ 15.7
Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	2 years 7 months 6 days