Income Taxes (Tables)
 12 Months Ended
Dec. 31, 2013
Income Tax Disclosure [Abstract]  
Schedule of provision for income taxes
The provision for annual income taxes consisted of the following (in thousands):
 
As of December 31,
 
2013
 
2012
 
2011
Current:
 
 
 
 
 
U.S. Federal
$
—

 
$
—

 
$
—

State
1

 
1

 
1

Foreign
16

 
50

 
42

Total current
$
17

 
$
51

 
$
43

Deferred:
 
 
 
 
 
U.S. Federal
$
—

 
$
—

 
$
—

State
—

 
—

 
—

Foreign
—

 
—

 
—

Total deferred
—

 
—

 
—

Total provision for income taxes
$
17

 
$
51

 
$
43
Reconciliation of federal statutory income tax
The reconciliation of federal statutory income tax to the Company's provision for income taxes is as follows (in thousands):
 
As of December 31,
 
2013
 
2012
 
2011
Expected provision at statutory federal rate
$
(3,080
)
 
$
(247
)
 
$
(10,482
)
State tax—net of federal benefit
1

 
1

 
1

U.S. federal research credit
(2,272
)
 
—

 
(870
)
Non deductible expenses
28

 
131

 
763

Others
(9
)
 
31

 
6

Change in valuation allowance
5,349

 
135

 
10,625

Provision for income taxes
$
17

 
$
51

 
$
43
Schedule of deferred tax assets and liabilities
Significant components of the Company's deferred tax assets and liabilities are as follows (in thousands):
 
As of December 31,
 
2013
 
2012
Deferred tax assets:
 
 
 
Net operating loss federal and state
$
15,411

 
$
12,515

Research and foreign tax credits
8,727

 
5,810

Accrued compensation and vacation
595

 
1,201

Deferred revenue, other accruals and reserves
2,188

 
574

Stock-based compensation
3,262

 
1,822

Patents
5,929

 
8,118

Gross deferred tax assets
36,112

 
30,040

Valuation allowance
(35,496
)
 
(29,199
)
Total deferred tax asset
616

 
841

Deferred tax liabilities:
 
 
 
Property and equipment
616

 
841

Total deferred tax liabilities
616

 
841

Net deferred tax assets
$
—

 
$
—
Schedule of unrecognized tax benefits roll forward
The following table summarizes the activity related to unrecognized tax benefits (in thousands):
 
As of December 31,
 
2013
 
2012
 
2011
Unrecognized benefit—beginning of period
$
1,840

 
$
1,401

 
$
1,067

Gross increase—prior period tax positions
274

 
38

 
—

Gross decreases—prior period tax positions
(90
)
 
—

 
(113
)
Gross increases—current period tax positions
632

 
401

 
447

Unrecognized benefit—end of period
$
2,656

 
$
1,840

 
$
1,401