CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Operating activities:
Net loss	$ (22,106)	$ (8,917)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation	208	275
Stock-based compensation	2,742	2,355
Deferred rent expense	588	0
Other	(151)	54
Changes in operating assets and liabilities	(7,122)	28,584
Net cash (used in) provided by operating activities	(25,841)	22,351
Investing activities:
Purchases of property and equipment	(1,054)	(808)
Proceeds from maturity of investments	35,647	10,974
Purchases of investments	(26,997)	(67,222)
Net cash provided by (used in) investing activities	7,596	(57,056)
Financing activities:
Proceeds from exercise of stock options	97	839
Proceeds from exercise of warrants	5	182
Proceeds from employee stock purchase plan	178	0
Issuance of common stock, net of issuance costs	0	47,207
Net cash provided by financing activities	280	48,228
Effect of exchange rate change on cash and cash equivalents	(2,001)	(825)
Net (decrease) increase in cash and cash equivalents	(19,966)	12,698
Cash and cash equivalents at beginning of period	74,867	37,878
Cash and cash equivalents at end of period	54,901	50,576
Supplemental cash flow disclosures:
Net unrealized gain on investments	93	1,667
Property and equipment included in accounts payable	$ 31	$ 202