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Stock-Based Compensation - Summary of ESPP Share Activity (Detail) - 2009 Employee Stock Purchase Plan [Member]
6 Months Ended
Jun. 30, 2016
shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Available for future purchases, January 1, 2016 279,589
Additional shares reserved under 2009 ESPP 82,084
Purchases (59,159)
Available for future purchases, June 30, 2016 302,514