Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities
Net loss	$ (41,924)	$ (31,130)
Adjustments to reconcile net loss to net cash used in operating activities:
Non-cash other expense, net	(3)	91
Non-cash interest income	28	(50)
Non-cash interest expense	371
Depreciation and amortization expense	245	262
Amortization of right-of-use assets	211
Stock-based compensation	3,728	2,011
Other, net	(20)	(5)
Changes in operating assets and liabilities:
Changes in long-term receivables	(282)	(3)
Changes in other receivables and prepaid expenses	392	(2,510)
Changes in accounts payable	(346)	(2,241)
Changes in accrued expenses and other liabilities	(4,106)	(142)
Changes in other non-current liabilities	(52)	33
Changes in income tax liabilities	10	324
Net cash used in operating activities	(41,748)	(33,360)
Cash flows from investing activities
Purchases of plant and equipment and intangible assets	(57)	(168)
Purchases of available-for-sale securities	(15,000)
Purchases of term deposits		(115)
Net cash used in investing activities	(15,057)	(283)
Cash flows from financing activities
Proceeds from at the market facility	13,592	22,784
Proceeds from long-term debt	80	410
Proceeds from employee share purchase plan	170
Equity transaction costs	(414)	(976)
Net cash provided by financing activities	13,428	22,218
Effects of foreign currency translation on cash and cash equivalents	40	(91)
Net decrease in cash and cash equivalents	(43,337)	(11,516)
Cash and cash equivalents at beginning of period	102,003	86,769
Cash and cash equivalents at end of period	58,666	75,253
Supplemental disclosures of cash flow information
Interest paid	1,109
Equity transaction costs incurred in prior periods and paid in current period	18	28
Equity transaction costs included in accounts payable and accrued expenses	$ 498	$ 119