Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement [Abstract]
Revenue (net of a $2,500 reduction of revenue in 2011 relating to common stock warrants)	$ 185,129	$ 117,914	$ 73,022
Cost of revenue	53,548	34,591	21,285
Gross profit	131,581	83,323	51,737
Operating expenses:
Sales and marketing	109,737	73,563	45,773
Research and development	21,260	14,886	10,149
General and administrative	33,572	25,912	15,122
Amortization of certain acquired intangible assets	1,004	739	0
Total operating expenses	165,573	115,100	71,044
Loss from operations	(33,992)	(31,777)	(19,307)
Other income (expense):
Interest income	357	0	20
Interest expense	(6,563)	(442)	(902)
Change in fair value of preferred stock warrant liabilities	0	0	(42,559)
Withdrawn secondary offering expense	0	0	(555)
Other, net	(356)	40	(416)
Other income (expense), net	(6,562)	(402)	(44,412)
Loss before income tax benefit (provision)	(40,554)	(32,179)	(63,719)
Income tax benefit (provision)	128	789	(181)
Net loss	(40,426)	(31,390)	(63,900)
Accretion of redeemable preferred stock	0	0	(5,208)
Net loss attributable to common stockholders	$ (40,426)	$ (31,390)	$ (69,108)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.79)	$ (0.63)	$ (1.74)
Weighted average common shares outstanding, basic and diluted	51,427	49,929	39,824