Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash flows from operating activities:
Net loss	$ (26,028)	$ (8,350)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Consulting services paid in common stock		37
Depreciation and amortization expense	507	77
Stock-based compensation expense	886	49
Non-cash interest expense	7	1
Changes in operating assets and liabilities:
Accounts receivable	(118)	(1,236)
Prepaid expenses and other current assets	(1,290)	(187)
Accrued expenses and other current liabilities and amounts due to related parties	1,633	(588)
Accounts payable	54	651
Deferred revenue	72	19,948
Other liabilities	64
Net cash (used in) provided by operating activities	(24,213)	10,402
Cash flows from investing activities:
Purchases of property and equipment	(2,186)	(1,198)
Lease deposits	62	(62)
Net cash used in investing activities	(2,124)	(1,260)
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs	79,219	4,875
Proceeds from exercise of common stock options	5
Proceeds from issuance of notes payable and common stock warrant, net of issuance costs	194	1,127
Payments of initial public offering costs	(1,501)
Repayment of notes payable	(248)
Net cash provided by financing activities	77,669	6,002
Net increase in cash and cash equivalents	51,332	15,144
Cash and cash equivalents at beginning of period	17,913	4,507
Cash and cash equivalents at end of period	69,245	19,651
Supplemental disclosure of cash flow information:
Interest paid	68
Supplemental disclosure of non-cash investing and financing activities:
Accretion of convertible preferred stock to redemption value	23	52
Issuance of common stock warrant in connection with notes payable		5
Purchases of property and equipment included in accounts payable and accrued expenses	47	$ 322
Deferred offering costs included in accounts payable and accrued expenses	$ 1,007