Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

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

Summary of Stock-based Compensation Recognized, Common Stock Purchased, and Average Price

The table below summarizes the stock-based compensation recognized, common stock shares purchased by Company employees, and the average purchase price per share as part of the ESPP program during the years ended December 31, 2017, 2016, and 2015.



	Year Ended December 31,
	2017		2016		2015
Stock-based compensation expense	$	850	$	1,205	$	921
Common stock shares purchased by Company employees	446,490		394,120		355,557
Average purchase price per share	$	5.64	$	8.17	$	8.33

Schedule of Compensation Expense Included in COGS and Operating Expenses

Stock-based compensation expense included in cost of goods sold and operating expenses for years ended December 31, 2017, 2016, and 2015 was as follows:



	Year Ended December 31,
	2017		2016		2015
Cost of goods sold	$	828	$	944	$	1,000
Operating expenses:
Research and development	1,259		1,528		1,005
Clinical and regulatory affairs	770		672		858
Marketing and sales	3,796		4,335		3,237
General and administrative	4,991		4,807		3,155
Total operating expenses	$	10,816	$	11,342	$	8,255

Total	$	11,644	$	12,286	$	9,255

Schedule of Fair Value Assumptions of Stock Options Granted

The fair value of stock options granted was estimated at the date of grant using the Black-Scholes option-pricing model. The following assumptions were used to determine fair value for the stock awards granted in the applicable year:



	Year Ended December 31,
	2017	2016	2015
Average expected option life (in years) (a)	5.6	5.5	5.5
Volatility (b)	51.3%	44.2%	43.3%
Risk-free interest rate (c)	1.9%	1.2%	1.6%
Dividend yield (d)	—	—	—
Weighted-average grant-date fair value per stock option	$2.51	$3.45	$6.37

(a) Determined by the historical stock option exercise behavior of the Company's employees (maximum term is 10 years).

(b) Measured using daily price observations for a period equal to the stock options' expected terms.

(d) The Company has never paid cash dividends on its common stock and does not expect to declare any cash dividends.

Schedule of Stock Option Activity

Stock option activity during the year ended December 31, 2017 is as follows:



	Number of Stock Options	Weighted Average Exercise Price	Weighted- Average Remaining Contractual Life (Years)		Aggregate Intrinsic Value
Outstanding — January 1, 2017	8,673,215	9.22
Granted	5,370,408	5.44
Exercised	(129,478)	4.21		(a)	$	226
Forfeited	(1,405,534)	8.20
Expired	(684,279)	11.38
Outstanding — December 31, 2017	11,824,332	$7.56	7.1	(b)	$	4,570
Vested and Expected to Vest — December 31, 2017	10,629,743	7.67	6.9	(b)	$	4,173
Vested — December 31, 2017	5,041,775	8.48	4.9	(b)	$	2,530

(a) Represents the total difference between the Company's stock price at the time of exercise and the stock option exercise price, multiplied by the number of options exercised.

(b) Represents the total difference between the Company's closing stock price on the last trading day of period reported on and the stock option exercise price, multiplied by the number of in-the-money options as of the period reported on. The amount of intrinsic value will change based on the fair market value of the Company's stock.

Schedule of Outstanding Stock Option Grants

The following table summarizes information regarding outstanding stock option grants as of December 31, 2017:



					Outstanding				Exercisable
Range of Exercise Prices					Granted Stock Options Outstanding	Weighted- Average Remaining Contractual Life (Years)	Weighted- Average Exercise Price		Granted Stock Options Exercisable	Weighted- Average Exercise Price
$	1.64	—	$	4.42	2,390,446	5.6	$	3.76	1,135,219	$	3.27
4.49		—	6.62		3,626,065	8.6	5.72		691,585	5.72
6.66		—	7.53		2,865,141	7.6	7.39		1,298,962	7.40
7.57		—	15.51		2,373,560	5.9	12.22		1,543,700	12.52
15.53		—	17.58		569,120	6.3	16.58		372,309	16.53
$	1.64	—	$	17.58	11,824,332	7.1	$	7.56	5,041,775	$	8.48

Summary of Activity and Related Information for Restricted Stock Awards

The following table summarizes activity and related information for the Company's restricted stock awards:



	Number of Restricted Stock Awards(2)		Weighted Average Fair Value per Share at Grant Date		Grant Date Fair Value		Vest Date Fair Value(1)
Unvested as of December 31, 2016	1,310,019		$	10.19
Granted	1,590,662		5.01		$	7,969
Forfeited	(470,626	)	9.74
Vested	(293,612	)	11.39				$	1,757
Unvested as of December 31, 2017	2,136,443		$	6.27

(1) Represents the Company's stock price on the vesting date multiplied by the number of vested shares.

(2) Shares granted in 2017 include 513,011 performance stock units that have certain performance conditions required to be achieved to vest.