Common Stock - Reserved Shares of Common Stock (Detail) - shares shares in Thousands	Sep. 30, 2016	Dec. 31, 2015	Feb. 28, 2013
Class Of Stock [Line Items]
Reserved shares of Common Stock	14,618	12,925
Shares Available for Future Issuance under ESPP [Member]
Class Of Stock [Line Items]
Reserved shares of Common Stock	1,307	776	1,000
RSUs [Member]
Class Of Stock [Line Items]
Reserved shares of Common Stock	1,975	1,221
Options Outstanding [Member]
Class Of Stock [Line Items]
Reserved shares of Common Stock	6,344	5,960
Shares to be issued in connection with acquisition of SocialMoov [Member]
Class Of Stock [Line Items]
Reserved shares of Common Stock	464	927
Options or RSUs Available for Future Grant [Member]
Class Of Stock [Line Items]
Reserved shares of Common Stock	4,528	4,041