Common Stock - Reserved Shares of Common Stock (Detail) - shares shares in Thousands	Mar. 31, 2017	Dec. 31, 2016	Feb. 28, 2013
Class Of Stock [Line Items]
Reserved shares of Common Stock	15,975	14,281
Shares Available for Future Issuance under Employee Stock Purchase Plan [Member]
Class Of Stock [Line Items]
Reserved shares of Common Stock	1,578	1,190	1,000
RSUs [Member]
Class Of Stock [Line Items]
Reserved shares of Common Stock	2,544	3,003
Options Outstanding [Member]
Class Of Stock [Line Items]
Reserved shares of Common Stock	3,259	3,749
Shares to be Issued in Connection with Acquisition of SocialMoov [Member]
Class Of Stock [Line Items]
Reserved shares of Common Stock	0	464
Options or Restricted Stock Units (RSUs) Available for Future Grant [Member]
Class Of Stock [Line Items]
Reserved shares of Common Stock	8,594	5,875