CONSOLIDATED STATEMENTS OF CHANGES IN CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($)	Common Stock.	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Total
Balance at Dec. 31, 2017	$ 2,000	$ 208,408,000	$ (41,000)	$ (123,534,000)	$ 84,835,000
Balance (in shares) at Dec. 31, 2017	21,041,250
Increase (Decrease) in Stockholders' Deficit
Issuance of common stock	$ 1,000	64,876,000			64,877,000
Issuance of stock (in shares)	8,117,647
Common stock issued on exercise of stock options		7,000			7,000
Common stock issued on exercise of stock options (in shares)	24,584
Vesting of restricted stocks issued upon early exercise of stock options		7,000			7,000
Stock-based compensation expense		1,801,000			1,801,000
Unrealized loss on marketable securities			2,000		2,000
Net loss				(14,301,000)	(14,301,000)
Balance at Mar. 31, 2018	$ 3,000	275,099,000	(39,000)	(137,835,000)	137,228,000
Balance (in shares) at Mar. 31, 2018	29,183,481
Balance at Dec. 31, 2018	$ 3,000	280,840,000	(34,000)	(170,473,000)	110,336,000
Balance (in shares) at Dec. 31, 2018	29,323,930
Increase (Decrease) in Stockholders' Deficit
Common stock issued on exercise of stock options	$ 2,970	1,000			1,000
Vesting of restricted stocks issued upon early exercise of stock options		5,000			5,000
Stock-based compensation expense		1,953,000			1,953,000
Unrealized loss on marketable securities			45,000		45,000
Net loss				(11,643,000)	(11,643,000)
Balance at Mar. 31, 2019	$ 3,000	$ 282,799,000	$ 11,000	$ (182,116,000)	$ 100,697,000
Balance (in shares) at Mar. 31, 2019	29,326,900