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Stub Period Comparative Data (Unaudited) (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended										6 Months Ended		12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016
Revenues:
Total revenues	$ 2,442	$ 486	$ 715	$ 928	$ 933	$ 385	$ 701	$ 590	$ 5,971	$ 277	$ 2,928	$ 1,318	$ 2,961	$ 7,539	$ 1,620
Operating expenses:
Research and development											10,412	8,088	16,178	14,880	14,381
General and administrative											8,901	5,044	11,545	11,235	9,013
Total operating expenses											27,487	13,132	29,235	26,115	23,394
Loss from operations	(11,005)	(13,554)	(9,782)	(4,678)	(5,808)	(6,006)	(6,136)	(5,160)	(94)	(7,186)	(24,559)	(11,814)	(26,274)	(18,576)	(21,774)
Interest and other income											367	49	101	91	72
Net loss	$ (11,594)	$ (33,126)	$ (34,428)	$ (6,978)	$ (5,782)	$ (5,983)	$ (6,116)	$ (5,140)	$ (67)	$ (7,162)	$ (44,720)	$ (11,765)	$ (53,171)	$ (18,485)	$ (21,547)
Net loss per common share - basic and diluted	$ (0.12)	$ (0.44)	$ (0.62)	$ (0.15)	$ (0.13)	$ (0.15)	$ (0.16)	$ (0.15)	$ 0	$ (0.21)	$ (0.53)	$ (0.28)	$ (1.15)	$ (0.52)	$ (0.68)
Weighted average common shares - basic and diluted	94,494	75,170	55,387	45,644	44,530	39,430	38,673	34,366	34,177	34,175	85,057	41,980	46,226	35,344	31,623
Collaborative Research and Development [Member]
Revenues:
Total revenues											$ 1,883	$ 601	$ 1,343	$ 6,569	$ 398
Royalty [Member]
Revenues:
Total revenues											$ 1,045	$ 717	$ 1,618	$ 970	$ 1,222