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Stock-based Compensation (Tables)
 12 Months Ended
Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Schedule of stock-based compensation expense
Stock-based compensation expense is included in the consolidated statements of operations as follows (in thousands):
 
 
Years Ended December 31,
 
2016
 
2015
 
2014
Research and development
$
1,033

 
$
935

 
$
953

Selling, general and administrative
4,640

 
4,191

 
3,667

 
$
5,673

 
$
5,126

 
$
4,620
Assumptions used to estimate the fair value of option grants
The following summarize the ranges of weighted-average assumptions used to estimate the fair value of employee stock options granted:
 
Years Ended December 31,
 
2016
 
2015
 
2014
Expected life (years)
5.3

 
6.1

 
6.0

Volatility
64.2
%
 
66.1
%
 
65.0
%
Risk-free interest rate
1.3
%
 
1.7
%
 
1.9
%
Expected dividend yield (1)
0.0
%
 
0.0
%
 
0.0
%
(1)
We do not currently pay dividends, and thus the dividend rate variable in the Black-Scholes-Merton option-pricing model is zero.
Schedule of share-based compensation, stock options, activity
The following table summarizes stock option activity in 2016:
 
Number
of
Shares
 
Weighted
Average
Exercise Price Per Share
 
Weighted
Average
Remaining
Contractual Term
 
Aggregate Intrinsic
Value
 
(in thousands)
 
 
 
(in years)
 
(in thousands)
Balance at January 1, 2016
3,918

 
$
4.49

 
 
 
 
Granted
971

 
$
4.16

 
 
 
 
Exercised
(398
)
 
$
2.60

 
 
 
 
Forfeited/Expired
(601
)
 
$
5.76

 
 
 
 
Outstanding at December 31, 2016
3,890

 
$
4.40

 
6.54
 
$
4,494

 
 
 
 
 
 
 
 
Exercisable at December 31, 2016
2,477

 
$
4.84

 
5.31
 
$
3,138

Vested and expected to vest at December 31, 2016
3,693

 
$
4.42

 
6.40
 
$
4,381
Schedule of share-based compensation, RSA activity
The following table summarizes the RSAs activity in 2016:
 
Number
of
Shares
 
Weighted Average
Grant Date
Fair Value
Per Share
 
(in thousands)
 
 
Non-vested balance at January 1, 2016
480

 
$
3.29

Granted
185

 
$
4.21

Vested
(435
)
 
$
3.40

Forfeited/Expired
—

 
$
—

Non-vested balance at December 31, 2016
230

 
$
3.82
Schedule of share-based compensation, RSU activity
The following table summarizes the RSUs activity in 2016:
 
Number
of
Shares
 
Weighted Average
Grant Date
Fair Value
Per Share
 
(in thousands)
 
 
Non-vested balance at January 1, 2016
545

 
$
3.15

Granted
330

 
$
4.10

Vested
(243
)
 
$
3.11

Forfeited/Expired
(15
)
 
$
2.74

Non-vested balance at December 31, 2016
617

 
$
3.69
Share-based compensation, performance shares sward outstanding activity
The following table summarizes the PSUs activity in 2016:
 
Number
of
Shares
 
Weighted Average
Grant Date
Fair Value
Per Share
 
(in thousands)
 
 
Non-vested balance at January 1, 2016
989

 
$
2.94

Granted
629

 
$
4.10

Vested
(482
)
 
$
2.89

Forfeited/Expired
(305
)
 
$
2.82

Non-vested balance at December 31, 2016
831

 
$
3.88