Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities
Net loss	$ (26,733)	$ (28,999)	$ (27,953)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	7,220	5,572	4,335
Stock-based compensation expense	12,499	7,527	2,426
Charge related to execution of new lease agreement	884
Loss on impairment and disposal of long-lived assets			811
Changes in operating assets and liabilities:
(Increase) decrease in accounts receivable, net	(625)	1,485	(1,587)
(Increase) decrease in advance to clients	(875)	(1,094)	415
(Increase) in prepaid expenses and other current assets	(4,001)	(374)	(939)
Increase (decrease) in accounts payable	2,251	(2,565)	1,894
Increase in accrued compensation and related benefits	4,317	3,123	3,924
Increase in accrued expenses and other liabilities	1,216	2,978	1,762
Increase in deferred revenue	703	640	530
Increase in payments to clients	(3,664)	(826)
(Increase) decrease in other assets and other liabilities, net	(2,709)	153	(1,267)
Other	250	695	(33)
Net cash used in operating activities	(9,267)	(11,685)	(15,682)
Cash flows from investing activities
Purchases of property and equipment	(4,096)	(3,803)	(2,367)
Capitalized content development cost expenditures	(9,518)	(7,150)	(5,213)
Other	(2,331)	(29)	(56)
Net cash used in investing activities	(15,945)	(10,982)	(7,636)
Cash flows from financing activities
Proceeds from issuance of common stock, net of offering costs	117,112	100,302
Proceeds from exercise of stock options	5,336	2,282	325
Proceeds from revolving line of credit		5,000
Payment on revolving line of credit		(5,000)
Proceeds from issuance of Series D redeemable convertible preferred stock, net of issuance costs			4,994
Other	(436)		(179)
Net cash provided by financing activities	122,012	102,584	5,140
Net increase (decrease) in cash and cash equivalents	96,800	79,917	(18,178)
Cash and cash equivalents, beginning of period	86,929	7,012	25,190
Cash and cash equivalents, end of period	183,729	86,929	7,012
Supplemental disclosure of non-cash investing and financing activities
Accretion of issuance costs on redeemable convertible preferred stock		89	347
Accrued capital expenditures	$ 415	557	216
Deferred offering costs included in accounts payable and accrued expenses			(1,057)
Issuance of Series D redeemable convertible preferred stock warrant in connection with revolving line of credit			$ 107
Common stock granted in exchange for consulting services received		$ 55