CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net loss	$ (31,063)	$ (26,018)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	270	264
Loss on disposal of fixed assets	248
Change in fair value of derivative liabilities		(1,547)
Share-based compensation	1,980	1,054
Unrealized foreign currency transaction (gain) loss	237	(93)
Accretion of discount on marketable securities	(346)
Changes in operating assets and liabilities:
Other receivables	679	(233)
Prepaid expenses and other current assets	706	204
Tax incentive receivables	980	(806)
Accounts payable	(2,088)	(112)
Accrued expenses and other current liabilities	2,372	1,011
Deferred rent	(91)	(95)
Net cash used in operating activities	(26,116)	(26,371)
Cash flows from investing activities:
Purchases of marketable securities	(104,421)
Proceeds from maturities of marketable securities	14,000
Purchases of property and equipment	(22)
Net cash used in investing activities	(90,443)
Cash flows from financing activities:
Proceeds from stock option exercises	197
Cash payment for Potentiator non-controlling interests		(1,175)
Net cash provided by (used in) financing activities	69,701	41,429
Net (decrease) increase in cash and cash equivalents	(46,858)	15,058
Cash, cash equivalents and restricted cash at beginning of period	87,338	10,365
Cash, cash equivalents and restricted cash at end of period	40,480	25,423
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property and equipment in accrued expenses	1,628	28
Deferred offering costs included in accounts payable and accrued expenses		1,588
Conversion of bridge units into preferred units		8,500
Settlement of derivative liabilities upon issuance of preferred units		944
Cumulative dividends on redeemable convertible preferred units		5,313
Accretion of redeemable convertible preferred units to redemption value		557
Accretion of bridge units to redemption value		576
Elimination of non-controlling interest balance upon repurchase of the non-controlling interest		5,306
2018 Equity Offering [Member]
Cash flows from financing activities:
Proceeds from equity offering	70,500
Payment of offering costs	$ (996)
2017 Initial Public Offering [Member]
Cash flows from financing activities:
Payment of offering costs		(507)
Series C Preferred Stock [Member]
Cash flows from financing activities:
Proceeds from issuance of preferred units, net of issuance costs		$ 43,111