Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (21,356)	$ (12,631)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,012	660
Equity-based compensation	4,107	2,630
Changes in operating assets and liabilities:
Accounts receivable	3,005	4,011
Prepaid expenses and other current assets	1,205	704
Accounts payable	59	(954)
Accrued expenses	(1,609)	(1,893)
Deferred revenue	(4,474)	(4,278)
Other assets	318	268
Other long-term liabilities	(37)	85
Net cash used in operating activities	(17,770)	(11,398)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(1,850)	(4,162)
Net cash used in investing activities	(1,850)	(4,162)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from options exercised	6,720	47
Net cash provided by financing activities	6,720	47
Net decrease in cash and cash equivalents	(12,900)	(15,513)
Cash and cash equivalents, beginning of period	340,678	273,064
Cash and cash equivalents, end of period	327,778	257,551
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Purchases of property and equipment unpaid at period end	$ 703	$ 378