Stock Based Compensation (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2014 USD ($) $ / shares	Jun. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2014 USD ($) $ / shares shares	Dec. 31, 2014 $ / shares shares	Feb. 05, 2014 $ / shares
Share based compensation, shares authorized under significant ranges of outstanding stock option plans in period [Abstract]
Closing price of the common stock (in dollars per share) | $ / shares						$ 6.50
Employees [Member]
Share-based compensation arrangement by share-based payment award, fair value assumptions and methodology [Abstract]
Estimated annualized forfeiture rate (in hundredths)			10.00%	12.00%
Employees and Directors [Member]
Share-based compensation arrangement by share-based payment award, fair value assumptions and methodology [Abstract]
Unrecognized compensation expense related to unvested stock options, granted | $	$ 4,900,000		$ 4,900,000
Unrecognized compensation cost, recognized as expense over a weighted-average period			1 year 11 days
Senior management [Member]
Share-based compensation arrangement by share-based payment award, fair value assumptions and methodology [Abstract]
Estimated annualized forfeiture rate (in hundredths)			2.00%	2.00%
Directors and nonemployees [Member]
Share-based compensation arrangement by share-based payment award, fair value assumptions and methodology [Abstract]
Estimated annualized forfeiture rate (in hundredths)			0.00%	0.00%
Stock Options [Member]
Share-based compensation arrangement by share-based payment award, fair value assumptions and methodology [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Method Used			Black-Scholes option-pricing model
Contractual term			10 years
Number of Options (Employees and Non-Employees) [Abstract]
Outstanding at beginning of period (in shares)			10,040,735
Granted (in shares)			550,000	300,000
Expired (in shares)			(124,429)
Outstanding at end of period (in shares)	10,466,306		10,466,306
Options exercisable at end of period (in shares)	6,911,989		6,911,989
Weighted-Average Exercise Price Options [Abstract]
Outstanding at beginning of period (in dollars per share) | $ / shares			$ 2.87
Granted (in dollars per share) | $ / shares			3.86
Expired | $ / shares			6.90
Outstanding at end of period (in dollars per share) | $ / shares	$ 3.33		3.33
Options exercisable at end of period (in dollars per share) | $ / shares	$ 3.59		$ 3.59
Share based compensation, shares authorized under significant ranges of outstanding stock option plans in period [Abstract]
Total Number of Options (in shares)	10,466,306		10,466,306
Weighted-Average Remaining Contractual Life			8 years 1 month 28 days
Weighted-Average Exercise Price (in dollars per share) | $ / shares	$ 3.33		$ 3.33
Total Number of Options Exercisable (in shares)	6,911,989		6,911,989
Weighted-Average Remaining Contractual Life			7 years 8 months 26 days
Weighted-Average Exercise Price, Options Exercisable (in dollars per share) | $ / shares	$ 3.59		$ 3.59
The aggregate intrinsic value of outstanding options | $	$ 10,200,000		$ 10,200,000
Aggregate intrinsic value of options vested | $			$ 6,100,000
Closing price of the common stock (in dollars per share) | $ / shares	$ 3.72		$ 3.72
Stock Options [Member] | Employees [Member]
Number of Options (Employees and Non-Employees) [Abstract]
Outstanding at beginning of period (in shares)			9,348,952
Granted (in shares)			550,000
Expired (in shares)			(68,000)
Outstanding at end of period (in shares)	9,830,952		9,830,952
Options exercisable at end of period (in shares)	6,276,275		6,276,275
Stock Options [Member] | Non-Employees [Member]
Number of Options (Employees and Non-Employees) [Abstract]
Outstanding at beginning of period (in shares)			692,143
Granted (in shares)			0
Expired (in shares)			(56,429)
Outstanding at end of period (in shares)	635,714		635,714
Options exercisable at end of period (in shares)	635,714		635,714
Stock Options And Warrants [Member]
Share-based compensation arrangement by share-based payment award, fair value assumptions and methodology [Abstract]
Risk-free interest rate (in hundredths)			2.21%	1.92%
Expected dividend yield (in hundredths)			0.00%	0.00%
Stock Options And Warrants [Member] | Minimum [Member]
Share-based compensation arrangement by share-based payment award, fair value assumptions and methodology [Abstract]
Expected volatility (in hundredths)			78.20%	87.00%
Expected lives			6 years	6 years
Stock Options And Warrants [Member] | Maximum [Member]
Share-based compensation arrangement by share-based payment award, fair value assumptions and methodology [Abstract]
Expected volatility (in hundredths)			84.40%	89.60%
Expected lives			10 years	10 years
Stock Options And Warrants [Member] | Employees [Member]
Total stock-based compensation expense resulting from stock options and warrants [Abstract]
Allocated employee and non-employee stock-based compensation expense, Total | $	$ 2,137,282	$ 559,863	$ 3,428,624	$ 1,046,977
Stock Options And Warrants [Member] | Non-Employees [Member]
Total stock-based compensation expense resulting from stock options and warrants [Abstract]
Allocated employee and non-employee stock-based compensation expense, Total | $	140,533	160,629	234,084	352,620
Restricted Stock [Member]
Total stock-based compensation expense resulting from stock options and warrants [Abstract]
Allocated employee and non-employee stock-based compensation expense, Total | $	$ 0	$ 156,296	$ 0	$ 310,874
Warrants [Member]
Weighted-Average Exercise Price Options [Abstract]
Share-based compensation arrangement by share-based payment award, shares issued in period (in shares)				25,000
Exercise price of warrants (in dollars per share) | $ / shares		$ 5.60		$ 5.60
Share based compensation, shares authorized under significant ranges of outstanding stock option plans in period [Abstract]
Warrants outstanding (in shares)	7,282,617		7,282,617		7,349,760
Weighted-average exercise price of warrants outstanding (in dollars per share) | $ / shares	4.29		4.29		4.27
Range $ 1.83 - 2.50 [Member] | Stock Options [Member]
Share based compensation, shares authorized under significant ranges of outstanding stock option plans in period [Abstract]
Range of Exercise Prices, Lower Range (in dollars per share) | $ / shares			$ 1.83
Range of Exercise Prices, Upper Range (in dollars per share) | $ / shares			$ 2.50
Total Number of Options (in shares)	5,837,558		5,837,558
Weighted-Average Remaining Contractual Life			8 years 6 months 4 days
Weighted-Average Exercise Price (in dollars per share) | $ / shares	$ 2.12		$ 2.12
Total Number of Options Exercisable (in shares)	3,226,398		3,226,398
Weighted-Average Remaining Contractual Life			8 years
Weighted-Average Exercise Price, Options Exercisable (in dollars per share) | $ / shares	$ 2.08		$ 2.08
Range $ 2.51 - 3.50 [Member] | Stock Options [Member]
Share based compensation, shares authorized under significant ranges of outstanding stock option plans in period [Abstract]
Range of Exercise Prices, Lower Range (in dollars per share) | $ / shares			2.51
Range of Exercise Prices, Upper Range (in dollars per share) | $ / shares			$ 3.50
Total Number of Options (in shares)	954,482		954,482
Weighted-Average Remaining Contractual Life			8 years 7 months 20 days
Weighted-Average Exercise Price (in dollars per share) | $ / shares	$ 2.85		$ 2.85
Total Number of Options Exercisable (in shares)	874,482		874,482
Weighted-Average Remaining Contractual Life			8 years 7 months 13 days
Weighted-Average Exercise Price, Options Exercisable (in dollars per share) | $ / shares	$ 2.83		$ 2.83
Range $ 3.51 - 8.00 [Member] | Stock Options [Member]
Share based compensation, shares authorized under significant ranges of outstanding stock option plans in period [Abstract]
Range of Exercise Prices, Lower Range (in dollars per share) | $ / shares			3.51
Range of Exercise Prices, Upper Range (in dollars per share) | $ / shares			$ 8.00
Total Number of Options (in shares)	3,386,201		3,386,201
Weighted-Average Remaining Contractual Life			7 years 11 months 5 days
Weighted-Average Exercise Price (in dollars per share) | $ / shares	$ 5.06		$ 5.06
Total Number of Options Exercisable (in shares)	2,523,043		2,523,043
Weighted-Average Remaining Contractual Life			7 years 8 months 26 days
Weighted-Average Exercise Price, Options Exercisable (in dollars per share) | $ / shares	$ 5.16		$ 5.16
Range $ 8.01 - 32.55 [Member] | Stock Options [Member]
Share based compensation, shares authorized under significant ranges of outstanding stock option plans in period [Abstract]
Range of Exercise Prices, Lower Range (in dollars per share) | $ / shares			8.01
Range of Exercise Prices, Upper Range (in dollars per share) | $ / shares			$ 32.55
Total Number of Options (in shares)	288,065		288,065
Weighted-Average Remaining Contractual Life			2 years 3 months 22 days
Weighted-Average Exercise Price (in dollars per share) | $ / shares	$ 9.00		$ 9.00
Total Number of Options Exercisable (in shares)	288,066		288,066
Weighted-Average Remaining Contractual Life			2 years 3 months 22 days
Weighted-Average Exercise Price, Options Exercisable (in dollars per share) | $ / shares	$ 9.00		$ 9.00
Research and Development Expense [Member] | Stock Options And Warrants [Member] | Employees [Member]
Total stock-based compensation expense resulting from stock options and warrants [Abstract]
Allocated employee and non-employee stock-based compensation expense, Total | $	$ 392,842	$ 234,484	$ 728,780	$ 409,638
Research and Development Expense [Member] | Stock Options And Warrants [Member] | Non-Employees [Member]
Total stock-based compensation expense resulting from stock options and warrants [Abstract]
Allocated employee and non-employee stock-based compensation expense, Total | $	0	0	0	0
General and Administrative Expense [Member] | Stock Options And Warrants [Member] | Employees [Member]
Total stock-based compensation expense resulting from stock options and warrants [Abstract]
Allocated employee and non-employee stock-based compensation expense, Total | $	1,744,440	325,379	2,699,844	637,339
General and Administrative Expense [Member] | Stock Options And Warrants [Member] | Non-Employees [Member]
Total stock-based compensation expense resulting from stock options and warrants [Abstract]
Allocated employee and non-employee stock-based compensation expense, Total | $	$ 140,533	$ 160,629	$ 234,084	$ 352,620
2000 Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, shares subject to stock options (in shares)	600,000		600,000
Expiration date			Aug. 06, 2010
Share-based compensation, shares available for future grant (in shares)	0		0
2008 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, shares subject to stock options (in shares)	9,900,000		9,900,000
Share-based compensation, shares available for future grant (in shares)	10,100,000		10,100,000
2008 Stock Incentive Plan [Member] | Restricted Stock [Member] | Senior management [Member]
Weighted-Average Exercise Price Options [Abstract]
Restricted stock granted (in shares)			100,000
Value of restricted shares issued | $	$ 627,000		$ 627,000