Common Stock - Reserved Shares of Common Stock (Detail) - shares shares in Thousands	Sep. 30, 2015	Dec. 31, 2014	Feb. 28, 2013
Class Of Stock [Line Items]
Reserved shares of Common Stock	13,249	11,304
Shares Available for Future Issuance under ESPP [Member]
Class Of Stock [Line Items]
Reserved shares of Common Stock	930	1,005	1,000
RSUs [Member]
Class Of Stock [Line Items]
Reserved shares of Common Stock	1,334	769
Options Outstanding [Member]
Class Of Stock [Line Items]
Reserved shares of Common Stock	6,400	6,376
Shares to be issued in connection with acquisition of SocialMoov [Member]
Class Of Stock [Line Items]
Reserved shares of Common Stock	927	0
Options or RSUs Available for Future Grant [Member]
Class Of Stock [Line Items]
Reserved shares of Common Stock	3,658	3,154