Annual report pursuant to Section 13 and 15(d)

CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT)

CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Stock Purchase Agreement	At The Market	Follow-On Offering [Member]	Private Placement	Series A convertible preferred stock	Series B convertible preferred stock	Common Stock [Member]	Common Stock [Member] Stock Purchase Agreement	Common Stock [Member] At The Market	Common Stock [Member] Follow-On Offering [Member]	Common Stock [Member] Private Placement	Common Stock [Member] Series A convertible preferred stock	Common Stock [Member] Series B convertible preferred stock	Additional Paid‑In Capital	Additional Paid‑In Capital Stock Purchase Agreement	Additional Paid‑In Capital At The Market	Additional Paid‑In Capital Follow-On Offering [Member]	Additional Paid‑In Capital Private Placement	Additional Paid‑In Capital Series A convertible preferred stock	Additional Paid‑In Capital Series B convertible preferred stock	Accumulated Other Comprehensive Loss	Accumulated Deficit
Balance at Dec. 31, 2015	$ (47,964)							$ 2							$ 5,547								$ (53,513)
Balance (in shares) at Dec. 31, 2015						30,350,000	16,893,931
Balance at Dec. 31, 2015						$ 29,015	$ 52,998
Balance (in shares) at Dec. 31, 2015								2,363,018
Issuance of convertible preferred stock, net of issuance costs							$ 39,794
Issuance of convertible preferred stock, net of issuance costs (in shares)							12,714,150
Conversion of convertible preferred stock into common stock						$ (29,015)	$ (92,792)
Conversion of convertible preferred stock into common stock (in shares)						(30,350,000)	(29,608,081)
Conversion of convertible preferred stock into common stock (in shares)													8,093,326	7,895,474
Conversion of convertible preferred stock into common stock						$ 29,015	$ 92,792						$ 8	$ 8						$ 29,007	$ 92,784
Exercise of stock options and vesting of restricted stock awards	395														395
Exercise of stock options and vesting of restricted stock awards (in shares)								429,070
Issuance of common stock, net of issuance costs	49,882							$ 5							49,877
Issuance of common stock, net of costs and fees (in shares)								4,600,000
Stock-based compensation expense	4,234														4,234
Other comprehensive gain (loss)	(9)																					$ (9)
Net loss	(47,743)																						(47,743)
Balance at Dec. 31, 2016	80,602							$ 23							181,844							(9)	(101,256)
Balance (in shares) at Dec. 31, 2016								23,380,888
Exercise of stock options and vesting of restricted stock awards	1,799														1,799
Exercise of stock options and vesting of restricted stock awards (in shares)								449,896
Issuance of common stock, net of issuance costs	32,547							$ 3							32,544
Issuance of common stock, net of costs and fees (in shares)								2,592,591
Stock-based compensation expense	4,419														4,419
Other comprehensive gain (loss)	(33)																					(33)
Net loss	(54,010)																						(54,010)
Balance at Dec. 31, 2017	$ 65,324							$ 26							220,606							(42)	(155,266)
Balance (in shares) at Dec. 31, 2017	26,423,375							26,423,375
Exercise of stock options	$ 626														626
Exercise of stock options, Shares	214,532							214,533
Issuance of common stock, net of issuance costs		$ 7,648	$ 16,538	$ 42,700	$ 1,380				$ 1	$ 1	$ 6					$ 7,647	$ 16,537	$ 42,694	$ 1,380
Issuance of common stock, net of costs and fees (in shares)									793,021	1,373,677	4,816,753	144,505
Stock-based compensation expense	$ 6,610														6,610
Other comprehensive gain (loss)	39																					39
Net loss	(62,279)																						(62,279)
Balance at Dec. 31, 2018	$ 78,586							$ 34							$ 296,100							$ (3)	$ (217,545)
Balance (in shares) at Dec. 31, 2018	33,765,864							33,765,864