Net Loss Per Share Attributable to Common Stockholders (Anti-Dilutive) (Details) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from net loss per share attributable to common stockholders	10,833	23,206	20,752
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from net loss per share attributable to common stockholders	8,113	8,360	5,771
Unvested restricted stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from net loss per share attributable to common stockholders	1,750	0	135
Unvested restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from net loss per share attributable to common stockholders	845	0	0
Shares held in escrow
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from net loss per share attributable to common stockholders	125	0	0
Conversion of convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from net loss per share attributable to common stockholders	0	14,410	14,410
Conversion of preferred stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from net loss per share attributable to common stockholders	0	436	436