Stock-based Compensation (Tables)

6 Months Ended

12 Months Ended

Jun. 30, 2016

Dec. 31, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-based Compensation Expense

	Three Months Ended			Three Months Ended			Six Months Ended			Six Months Ended
	June 30,			June 30,			June 30,			June 30,
	2016			2015			2016			2015
Research and development		$	284,057		$	284,125		$	587,681		$	325,701
General and administrative			673,506			1,104,883			1,903,770			1,146,079
Total stock-based compensation expense		$	957,563		$	1,389,008		$	2,491,451		$	1,471,780

	Years Ended December 31,
	2015		2014
Research and development	$	929,633	$	163,019
General and administrative		3,534,062		441,957
Total share-based compensation expense	$	4,463,695	$	604,976

Summary of Stock Option Activity

	Options Outstanding			Weighted Average Exercise Price
Outstanding at December 31, 2013		20,543		$	8.81
Granted		12,280			62.68
Exercised		—			—
Forfeited/cancelled/expired		—			—
Outstanding and expected to vest at December 31, 2014		32,823		$	29.00
Granted		407,547			16.50
Exercised		(376	)		2.15
Forfeited/cancelled/expired		(1,746	)		54.91
Outstanding and expected to vest at December 31, 2015		438,248		$	17.46
Vested and exercisable at December 31, 2015		24,054		$	26.57

Summary of activity related to restricted stock grants

	Shares		WeightedAverage Grant-Date Fair Value
Non-vested at December 31, 2014		—	$	—
Granted		310,926		16.87
Vested		—		—
Forfeited		—		—
Non-vested at December 31, 2015		310,926	$	16.87

Valuation Assumptions Used to Determine Stock-based Expense

	Years Ended December 31,
	2015			2014
Risk-free interest rate	0.9 to 1.8 %			0.1 to 2 %
Dividend yield		0	%		0	%
Expected volatility	81to87 %			84to100 %
Expected life of options, in years	5.5 and 6.0			5 and 6.25
Weighted average grant date fair value	$	1.56		$	4.73

Common Stock Reserved for Future Issuance

Common stock reserved for conversion of preferred stock	2,792,189
Common stock reserved for exercise of warrants	1,199,505
Common stock options outstanding	632,310
Authorized for future grant or issuance under the Stock Plan	205,546
Nonvested restricted stock	212,689
Total	5,042,239

Common stock reserved for conversion of preferred stock and warrants	4,012,442
Common stock options outstanding	438,249
Authorized for future grant or issuance under the Stock Plan	401,353
Unvested restricted stock	310,926
Total	5,162,970