Anti-dilutive Shares Excluded From Calculation of Diluted Net Loss Per Share Attributable to Common Stockholders (Detail) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from the calculation of diluted net loss per share	7,121	6,207
Options to purchase common stock and restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from the calculation of diluted net loss per share	7,059	5,797
Common stock subject to repurchase right
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from the calculation of diluted net loss per share	15	35
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from the calculation of diluted net loss per share	0	375
Shares issued for purchase consideration held in escrow
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from the calculation of diluted net loss per share	16	0
Other restricted common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from the calculation of diluted net loss per share	31	0