CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net loss	$ (61,447)	$ (27,397)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	537	105
Stock-based compensation expense	10,392	6,457
Change in fair value of contingent consideration	866
Changes in operating assets and liabilities:
Accounts receivable	(1,701)
Inventory	(1,026)
Prepaid expenses and other assets	2,345	(3,897)
Accounts payable	4,693	3,161
Accrued expenses	1,636	(1,168)
Net cash used in operating activities	(43,705)	(22,739)
Cash flows from investing activities:
Purchases of property and equipment	(650)	(388)
Purchases of marketable securities	(74,246)	(41,534)
Proceeds from sales and maturities of marketable securities	144,375	47,652
Net cash provided by investing activities	69,479	5,730
Cash flows from financing activities
Proceeds from sale of stock, net of issuance costs		19,311
Capital lease payments	(335)
Proceeds from the exercise of employee stock options	394	235
Net cash provided by financing activities	59	19,546
Net increase in cash and cash equivalents	25,833	2,537
Cash and cash equivalents at beginning of period	20,202	30,171
Cash and cash equivalents at end of period	46,035	32,708
Supplemental disclosures of non-cash investing and financing activities:
Additions to property and equipment included in accounts payable	442	$ 190
Property and equipment obtained pursuant to capital lease financing arrangements	1,896
Offering costs included in accounts payable	$ 20