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Stock-Based Compensation - Employee Stock Purchase Plan ("ESPP") - Additional Information (Detail) - USD ($)
$ in Millions
1 Months Ended 6 Months Ended
Feb. 28, 2015
Feb. 28, 2014
Jun. 30, 2015
Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Offering period     6 months  
Employee Stock Purchase Plan ("ESPP") [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Percentage of fair market value to determine purchase price     85.00%  
Proceeds of from issuance of shares under ESPP $ 0.4 $ 0.3    
Options issued 57,293 49,063    
Rate of discount on fair market value of common stock under ESPP     15.00%  
Period of expected life, options granted     5 years  
Increase number authorized shares       750,000