CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net loss	$ (45,589)	$ (36,604)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	221	80
Stock-based compensation expense	10,130	4,194
Non-cash charges related to Vixen acquisition		2,784
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(4,331)	110
Accounts payable	3,130	915
Accrued expenses	(14)	1,990
Net cash used in operating activities	(36,453)	(26,531)
Cash flows from investing activities:
Purchases of property and equipment	(658)	(170)
Acquisition of Confluence, net of cash acquired	(9,647)
Purchases of marketable securities	(120,496)	(33,747)
Proceeds from sales and maturities of marketable securities	96,674	49,832
Net cash provided by investing activities	(34,127)	15,915
Cash flows from financing activities
Proceeds from issuance of common stock in connection with private placement, net of issuance costs		18,547
Proceeds from sale of stock, net of issuance costs	19,311
Proceeds from issuance of common stock in connection with public offering, net of issuance costs	80,918
Proceeds from the exercise of employee stock options	235	14
Net cash provided by financing activities	100,464	18,561
Net increase in cash and cash equivalents	29,884	7,945
Cash and cash equivalents at beginning of period	30,171	9,851
Cash and cash equivalents at end of period	60,055	17,796
Supplemental disclosures of non-cash investing and financing activities:
Additions to property and equipment included in accounts payable	20	13
Fair value of stock issued in connection with acquisition	9,675	$ 2,355
Offering costs included in accounts payable	$ 107