Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Apr. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Subsidiary, Sale of Stock [Line Items]
Cash equivalents maturities, term		three months or less
Accumulated deficit		$ (293,069)	$ (292,275)
Cash		233	1,115	$ 6,041	$ 3,535
Current liabilities		$ 1,524	$ 1,649
Substantial doubt about going concern, management's evaluation		Mateon's existing cash to support its planned operations into the fourth quarter of 2018. Prior to this time, the Company will need to secure additional funding or could be forced to curtail or terminate operations. Because the Company does not currently have a guaranteed source of working capital that will sustain planned operations past the fourth quarter of 2018, Management has determined that there is substantial doubt about the Company's ability to continue as a going concern.
Subsequent Event [Member]
Subsidiary, Sale of Stock [Line Items]
Estimated net proceeds from private placement transaction	$ 2,400