Net Loss per Share (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Anti-Dilutive Securities
Shares not included in the computation of diluted net loss per share (in shares)	3,644,000	6,887,000	3,532,000	6,558,000
Share issuances under equity incentive plan and ESPP
Anti-Dilutive Securities
Shares not included in the computation of diluted net loss per share (in shares)	3,603,000	6,653,000	3,491,000	6,324,000
RSAs
Anti-Dilutive Securities
Shares not included in the computation of diluted net loss per share (in shares)	41,000	234,000	41,000	234,000
Performance-based vesting
Anti-Dilutive Securities
Shares not included in the computation of diluted net loss per share (in shares)	1,440,000		1,440,000