Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning Balance at Dec. 31, 2014	$ 106,117	$ 5	$ 253,251	$ (146,392)	$ (747)
Beginning Balance, shares at Dec. 31, 2014		5,026
Issuance of common stock from exercise of vested stock options, vesting of restricted stock units and vesting of options and shares subject to repurchase (Note 10)	$ 2,014	$ 0	2,014	0	0
Issuance of common stock from exercise of vested stock options, vesting of restricted stock units and vesting of options and shares subject to repurchase (Note 10), shares	104	192
Tax withholding related to vesting of restricted stock units	$ (571)	$ 0	(571)	0	0
Issuance of common stock under employee stock purchase plan	1,035	$ 0	1,035	0	0
Issuance of common stock under employee stock purchase plan, shares		37
Issuance of unrestricted common stock in connection with acquisition of SocialMoov S.A.S.	4,338	$ 0	4,338	0	0
Issuance of unrestricted common stock in connection with acquisition of SocialMoov S.A.S., shares		91
Stock issuance costs incurred in connection with acquisition of SocialMoov S.A.S.	(51)	$ 0	(51)	0	0
Stock-based compensation expense	15,619	0	15,619	0	0
Repurchase of unvested shares	(2)	$ 0	(2)	0	0
Repurchase of unvested shares, shares		0
Stock-based compensation tax benefits	3	$ 0	3	0	0
Net loss	(33,349)	0	0	(33,349)	0
Foreign currency translation adjustments and other, net	(1,022)	0	0	8	(1,030)
Ending Balance at Dec. 31, 2015	94,131	$ 5	275,636	(179,733)	(1,777)
Ending Balance, shares at Dec. 31, 2015		5,346
Issuance of common stock from exercise of vested stock options, vesting of restricted stock units and vesting of options and shares subject to repurchase (Note 10)	$ 570	$ 1	569	0	0
Issuance of common stock from exercise of vested stock options, vesting of restricted stock units and vesting of options and shares subject to repurchase (Note 10), shares	38	87
Tax withholding related to vesting of restricted stock units	$ (362)	$ 0	(362)	0	0
Issuance of common stock under employee stock purchase plan	548	$ 0	548	0	0
Issuance of common stock under employee stock purchase plan, shares		42
Issuance of unrestricted common stock in connection with acquisition of SocialMoov S.A.S.	0	$ 0	0	0	0
Issuance of unrestricted common stock in connection with acquisition of SocialMoov S.A.S., shares		66
Stock-based compensation expense	10,295	$ 0	10,295	0	0
Net loss	(16,480)	0	0	(16,480)	0
Foreign currency translation adjustments and other, net	(1,104)	0	6	0	(1,110)
Ending Balance at Dec. 31, 2016	87,598	$ 6	286,692	(196,213)	(2,887)
Ending Balance, shares at Dec. 31, 2016		5,541
Issuance of common stock from exercise of vested stock options, vesting of restricted stock units and vesting of options and shares subject to repurchase (Note 10)	11	$ 0	11	0	0
Issuance of common stock from exercise of vested stock options, vesting of restricted stock units and vesting of options and shares subject to repurchase (Note 10), shares		79
Tax withholding related to vesting of restricted stock units	(604)	$ 0	(604)	0	0
Issuance of common stock under employee stock purchase plan	362	$ 0	362	0	0
Issuance of common stock under employee stock purchase plan, shares		43
Issuance of unrestricted common stock in connection with acquisition of SocialMoov S.A.S.	0	$ 0	0	0	0
Issuance of unrestricted common stock in connection with acquisition of SocialMoov S.A.S., shares		66
Stock-based compensation expense	4,704	$ 0	4,704	0	0
Net loss	(31,491)	0	0	(31,491)	0
Foreign currency translation adjustments and other, net	2,203	0	(2)	0	2,205
Ending Balance at Dec. 31, 2017	$ 62,783	$ 6	$ 291,163	$ (227,704)	$ (682)
Ending Balance, shares at Dec. 31, 2017		5,729