Cover Page - shares	3 Months Ended
	Mar. 31, 2020	Apr. 30, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
Document Transition Report	false
Entity File Number	001-35006
Entity Registrant Name	SPECTRUM PHARMACEUTICALS INC
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	93-0979187
Entity Address, Address Line One	11500 South Eastern Avenue
Entity Address, Address Line Two	Suite 240
Entity Address, City or Town	Henderson
Entity Address, State or Province	NV
Entity Address, Postal Zip Code	89052
City Area Code	702
Local Phone Number	835-6300
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Title of 12(b) Security	Common Stock, $0.001 par value
Trading Symbol	SPPI
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		116,468,472
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Entity Central Index Key	0000831547
Current Fiscal Year End Date	--12-31