Net Loss Per Share Attributable to Common Stockholders - Anti-dilutive Shares Excluded From Calculation of Diluted Net Loss Per Share (Details) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from net loss per share attributable to common stockholders	17,106	7,388	6,005
Options to purchase common stock and restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from net loss per share attributable to common stockholders	7,730	7,331	5,845
Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from net loss per share attributable to common stockholders	4,682	0	0
Warrants | Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from net loss per share attributable to common stockholders	4,682	0	130
Shares issued for purchase consideration held in escrow
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from net loss per share attributable to common stockholders	0	16	0
Common Stock Repurchase Program
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from net loss per share attributable to common stockholders	0	10	30
Other restricted common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from net loss per share attributable to common stockholders	12	31	0