Stockholders' Equity (Summary of Nonvested Options) (Details) - $ / shares	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Options
Nonvested at beginning of period	5,202,095
Options granted	2,225,900
Options vested	(972,880)
Options forfeited	(15,235)
Nonvested at end of period	6,439,880
Weighted-Average Grant Date Fair Value
Nonvested at beginning of period (in dollars per share)	$ 3.44
Options granted (in dollars per share)	3.37	$ 3.53
Options vested (in dollars per share)	3.35
Options forfeited (in dollars per share)	4.89
Nonvested at end of period (in dollars per share)	$ 3.42