Description of Business, Basis of Presentation, and Operating Segment - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2018 Segment product
Segment Reporting Information [Line Items]
Number of late stage development products	3
Number of reportable operating segment | Segment	1
Spectrum Pharma Canada [Member]
Segment Reporting Information [Line Items]
Ownership interest, percentage	50.00%
Cancer Drugs [Member]
Segment Reporting Information [Line Items]
Number of products for sale	6