Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

The following table summarizes the Company’s stock option activity for 2017:



	Shares (in thousands)		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2016	3,285		$	15.46
Granted	961		$	11.07
Exercised	(677	)	$	15.47
Canceled	(177	)	$	11.79
Outstanding at December 31, 2017	3,392		$	14.41	7.2	$	86,987
Exercisable at December 31, 2017	2,003		$	16.53	6.3	$	47,116

The following table summarizes the Company’s restricted stock unit activity for 2017:



	Shares (in thousands)		Weighted Average Fair Value per Share at Grant Date
Nonvested at December 31, 2016	103		$	10.31
Granted	175		10.42
Vested	—		—
Canceled	(19	)	9.60
Nonvested at December 31, 2017	259		10.43

The assumptions used in the Black-Scholes option-pricing model were as follows:



	Year Ended December 31,
	2017	2016	2015
Stock Options
Risk free interest rate	1.8% to 2.3%	1.1% to 2.1%	1.5% to 1.9%
Expected term	5.1 to 6.1 years	5.1 to 6.1 years	5.1 to 6.1 years
Expected volatility	75.1% to 85.8%	76.5% to 78.1%	76.7% to 79.2%
Expected dividend yield	—%	—%	—%
Weighted-average fair value of option on grant date	$7.43	$6.69	$8.37

Employee Stock Purchase Plan
Risk free interest rate	1.1% to 1.6%	0.5% to 0.8%	0.1% to 0.5%
Expected term	0.5 to 1.0 years	0.5 to 1.0 years	0.5 to 1.0 years
Expected volatility	54.8% to 152.8%	59.5% to 71.3%	67.4% to 77.8%
Expected dividend yield	—%	—%	—%

The Company recognized stock-based compensation expense in continuing operations as follows (in thousands):



	Year Ended December 31,
	2017		2016		2015
Cost of contract manufacturing	$	71	$	386	$	390
Research and development	1,933		1,924		1,266
Selling, general and administrative	4,151		5,043		5,285
Total	$	6,155	$	7,353	$	6,941