Stockholders' Equity and Redeemable Non-controlling Interests (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance			$ 128,442
Issuance of common stock upon exercise and early exercise of stock options			3,296
Issuance of common stock under employee stock purchase plan			3,384
Investment by redeemable non-controlling interests			369
Withholding taxes for the net share settlement of equity awards			(1,698)
Vesting of early exercised options			190	410
Costs incurred with follow-on offering			62
Stock-based compensation expense			10,949
Net loss	(13,112)	(12,390)	(25,621)	(21,914)
Foreign currency translation adjustments			47
Balance	119,420		119,420
Redeemable Non-controlling Interests
Investment by redeemable non-controlling interests			1,585
Net loss	(159)		(170)
Foreign currency translation adjustments			18
Balance	$ 1,433		$ 1,433