STOCK-BASED COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2017

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

Schedule of Weighted Average Assumptions used to Estimate Fair Value of Stock Options Granted

A summary of the weighted-average assumptions used to estimate the fair values of the stock options granted during the periods presented is as follows:

	Years Ended December 31,
	2017			2016			2015
Expected term (in years)	4.4			4.5			4.5
Expected volatility	83.9		%	80.0		%	72.5		%
Annual risk-free rate of return	1.8		%	1.1		%	1.4		%
Dividend yield	—		%	—		%	—		%
Weighted-average fair value on grant date	$	0.76		$	1.29		$	4.68

Summary of Total Stock Based Compensation Expense Components

The following table summarizes the components of total stock-based compensation expense included in the consolidated statements of operations for the periods presented (in thousands):

	Years Ended December 31,
	2017		2016		2015
Cost of revenues	$	1,072	$	1,188	$	1,217
Research and development	2,573		3,879		4,559
Sales and marketing	1,157		2,144		3,162
General and administrative	1,925		3,115		3,758
Total stock-based compensation expense	$	6,727	$	10,326	$	12,696

Summary of Stock Based Compensation Expense Associated with Each Type of Award

A summary of stock-based compensation expense associated with each type of award for the periods presented is as follows (in thousands):

	Years Ended December 31,
	2017		2016		2015
Stock options and restricted stock units	$	5,559	$	8,384	$	10,685
ESPP	1,168		1,942		2,011
Total stock-based compensation expense	$	6,727	$	10,326	$	12,696

Summary of Stock Option Activity

A summary of the Company’s stock option activity for the periods presented is as follows (in thousands, except per share data):

	Shares		Weighted- Average Exercise Price per Share
Options outstanding — December 31, 2014	8,632		$	4.75
Granted	1,289		8.20
Exercised	(1,079	)	1.40
Canceled	(672	)	9.31
Options outstanding — December 31, 2015	8,170		5.36
Granted	2,440		2.12
Exercised	(375	)	0.39
Canceled	(1,505	)	6.01
Options outstanding — December 31, 2016	8,730		4.55
Granted	4,500		1.22
Exercised	(425	)	0.51
Canceled	(4,379	)	6.91
Options outstanding — December 31, 2017	8,426		1.77

Summary of Stock Options Outstanding

The following table summarizes information about stock options outstanding at December 31, 2017:

	Options Outstanding				Options Exercisable
Range of Exercise Prices	Number of Shares (in thousands)	Weighted- Average Remaining Life (in years)	Weighted- Average Exercise Price		Number of Shares (in thousands)	Weighted- Average Exercise Price
$0.27 —– $0.79	1,690	4.0	$	0.51	1,117	$	0.38
$0.83 —– $1.29	1,565	6.8	1.17		34	1.06
$1.31 —– $1.31	1,751	6.3	1.31		500	1.31
$1.37 —– $1.98	1,726	2.8	1.67		1,415	1.66
$2.00 —– $12.57	1,694	3.8	4.14		1,245	4.62
Total	8,426				4,311

Summary of Restricted Stock Unit Activity

A summary of restricted stock unit activity for the periods presented is as follows: (in thousands, except per share data):

	Restricted Stock Units		Weighted Average Fair Value per Share at Grant Date
Outstanding at December 31, 2014	1,345		$	8.25
Granted	683		11.22
Vested	(488	)	8.58
Canceled	(227	)	10.32
Outstanding at December 31, 2015	1,313		9.31
Granted	54		1.99
Vested	(464	)	9.06
Canceled	(297	)	8.32
Outstanding at December 31, 2016	606		9.33
Granted	5,418		1.46
Vested	(885	)	3.81
Canceled	(1,634	)	1.90
Outstanding at December 31, 2017	3,505		2.03

Summary of ESPP Activity

A summary of ESPP activity for the years presented is as follows: (in thousands, except per share data):

	Years Ended December 31,
	2017		2016		2015
Proceeds from common stock issued under ESPP	$	313	$	999	$	2,497
Shares of common stock issued	478		659		499
Weighted-average price per share	$	0.65	$	1.52	$	5.00