Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity

The following is a summary of option activity under the Stock Incentive Plans and Inducement Plan (in thousands, except share and per share amounts):

	Number of Shares			Weighted-Average Exercise Price Per Share		Weighted-Average Remaining Contractual Term (In years)		Aggregate Intrinsic Value
Outstanding at December 31, 2019		6,353,330		$	4.95		7.29	$	229
Granted		4,355,952			1.37
Exercised		(10,000	)		0.75
Forfeited		(864,757	)		3.61
Cancelled		(150,165	)		6.08
Outstanding at June 30, 2020		9,684,360		$	3.45		7.67	$	1,323
Exercisable at June 30, 2020		4,114,005		$	5.76		5.57	$	168
Vested or expected to vest at June 30, 2020		8,512,277		$	3.71		7.44	$	1,058

Schedule of Estimated Assumptions Used to Calculate Weighted-Average Grant Date Fair Value of Options Granted

There were 10,000 options exercised in the six months ended June 30, 2020 and no options exercised in the six months ended June 30, 2019. The weighted-average grant date fair values of stock options granted in the six month periods ended June 30, 2020 and 2019 were $0.69 per share and $1.93 per share, respectively, and were calculated using the following estimated assumptions:

	Six Months Ended
	June 30,
	2020			2019
Weighted-average risk-free interest rate		1.40	%		2.37	%
Expected dividend yield		—	%		—	%
Expected volatility		95	%		72	%
Expected terms	5.7 years			6.0 years

Schedule of Nonvested Restricted Stock Units Activity

The following is a summary of restricted stock unit activity under the 2014 Plan (in thousands, except share and per share amounts):

	Number of Shares			Weighted-Average Grant Date Fair Value
Nonvested at December 31, 2019		1,295,508			4.19
Granted		917,064			0.54
Vested		(331,433	)		3.45
Forfeited		(454,930	)		3.99
Nonvested at June 30, 2020		1,426,209			2.07

Summary of Stock-Based Compensation Expense for Stock Options Granted that was Recorded in the Company's Results of Operations

The following table summarizes the stock-based compensation expense resulting from awards granted under Stock Incentive Plans, the Inducement Plan and the 2014 Employee Stock Purchase Plan, that was recorded in the Company’s results of operations for the periods presented (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2020		2019		2020		2019
Cost of product revenue	$	4	$	—	$	80	$	49
Research and development		237		436		550		831
Selling, general and administrative		703		848		1,505		2,353
Total stock-based compensation expense	$	944	$	1,284	$	2,135	$	3,233