Financial Commitments and Contingencies and License Agreements - Additional Information (Details) $ in Thousands, € in Millions			1 Months Ended														2 Months Ended	3 Months Ended			5 Months Ended	12 Months Ended
	Jan. 08, 2016 USD ($)	Jul. 17, 2013 USD ($)	Sep. 30, 2017 USD ($)	Aug. 31, 2017 USD ($)	Jul. 31, 2017 USD ($) shares	Apr. 30, 2016 USD ($) shares	Jan. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jun. 30, 2014	Feb. 28, 2014 USD ($)	Sep. 30, 2012 USD ($)	Apr. 30, 2012 EUR (€)	Feb. 28, 2010 USD ($)	Nov. 30, 2009 USD ($)	Oct. 31, 2008 USD ($) shares	Jan. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2017 USD ($) shares	Dec. 31, 2017 USD ($) Country	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)	Nov. 30, 2014 USD ($)	May 31, 2006 USD ($)
Long-term Purchase Commitment [Line Items]
Rental expense																						$ 1,600	$ 1,500	$ 1,700
Potential payment based on achievement of sales milestones																						33,000
Acquisition-related contingent obligations																					$ 6,272	$ 6,272	1,315
Payment of all royalty obligations			$ 2,600
Amount receivable on approval of oral form of FUSILEV																										$ 200
Percentage of royalty on annual worldwide sales under condition one																					20.00%	20.00%
License fee and service revenue																					$ 0	$ 0	1,831
Ligand contingent consideration																					$ 0	0	$ 0
Additional license fees																						$ 60,000
Percentage of royalties on net sale of licensed products																						20.00%
Stock issued (shares) | shares					3,243,882																10,314,250		10,890,915
Consideration paid under agreement (shares)											$ 1,000
Proceeds from stock					$ 23,745																$ 104,527	$ 128,272	$ 73,869	0
Cash paid for income taxes																						17	11	$ 335
Accrued executive deferred compensation																					11,000	11,000
Accrued executive deferred compensation, current																					5,100	5,100
Accrued executive deferred compensation, noncurrent																					5,928	5,928	8,352
Allergan [Member]
Long-term Purchase Commitment [Line Items]
Up-front non-refundable payment																$ 41,500
License costs																$ 300
Nippon Kayaku [Member]
Long-term Purchase Commitment [Line Items]
Upfront fee															$ 15,000
Payment receivable on achievement of regulatory milestones																						10,000
Payment on achievement of commercialization milestones																						126,000
TopoTarget [Member]
Long-term Purchase Commitment [Line Items]
Payments receivable on achievement of potential sales milestones																					190,000	190,000
Payment of all royalty obligations														$ 30,000
Payment receivable on achievement of regulatory milestones																						88,000
Percentage of development cost														70.00%
Percentage of development cost that is funded by TopoTarget for joint development plan														30.00%
Additional payments based on the achievement of certain development											$ 10,000
Aggregate payout value																				$ 17,800
Second milestone payment																									$ 25,000
Common Class A [Member] | Allergan [Member]
Long-term Purchase Commitment [Line Items]
Stock issued (shares) | shares																25,000
Common stock issued under an at-market-issuance sales agreement (Note 7)																$ 100
Regulatory [Member]
Long-term Purchase Commitment [Line Items]
License fee and service revenue			$ 2,000
Regulatory [Member] | Maximum [Member]
Long-term Purchase Commitment [Line Items]
Milestone net sales achievement				$ 3,000
Potential milestone payments												$ 16,000										16,000
Commercial progress and sales-dependent [Member] | Maximum [Member]
Long-term Purchase Commitment [Line Items]
Potential milestone payments												$ 107,000										107,000
Milestone Payments [Member]
Long-term Purchase Commitment [Line Items]
Milestone net sales achievement		$ 30,000
Ligand contingent consideration						$ 6,000															$ 7,700	7,700
Milestone payments		5,000																				$ 60,000
FOLOTYN [Member]
Long-term Purchase Commitment [Line Items]
Percentage of royalty on annual worldwide sales under condition one																					8.00%	8.00%
Percentage of royalty on annual worldwide sales under condition two																					9.00%	9.00%
Percentage of royalty on annual worldwide sales under condition three																					11.00%	11.00%
FOLOTYN [Member] | Minimum [Member]
Long-term Purchase Commitment [Line Items]
Amount of annual worldwide sales on which royalty is payable under condition two																						$ 150,000
Amount of annual worldwide sales on which royalty is payable under condition three																						300,000
FOLOTYN [Member] | Maximum [Member]
Long-term Purchase Commitment [Line Items]
Amount of annual worldwide sales on which royalty is payable under condition one																						150,000
Amount of annual worldwide sales on which royalty is payable under condition two																						300,000
ZEVALIN [Member]
Long-term Purchase Commitment [Line Items]
Potential payment based on achievement of sales milestones																						5,000
Acquisition-related contingent obligations																					$ 100	$ 100	100
ZEVALIN [Member] | Licensing Agreements [Member]
Long-term Purchase Commitment [Line Items]
Fees paid to Bayer for acquiring licensing rights | €													€ 19
Minimum number of countries outside U.S. approved ZEVALIN for treatment | Country																						40
Percentage of royalty on net sales													20.00%									20.00%
Term													15 years
Up-front non-refundable payment									$ 500
Payments receivable on achievement of potential sales milestones																					1,500	$ 1,500
Aggregate amount receivable based on achievement of milestones																						3,000
Payment receivable on achievement of regulatory milestones																						1,500
Talon Therapeutics, Inc. [Member]
Long-term Purchase Commitment [Line Items]
Acquisition-related contingent obligations																					6,200	6,200	1,300
Contingent value rights future cash payments		$ 195,000																			195,000	195,000
SPI-2012 [Member]
Long-term Purchase Commitment [Line Items]
Potential payment based on achievement of sales milestones																						225,000
Potential payment based on achievement of regulatory milestones																						13,000
SPI-2012 [Member]
Long-term Purchase Commitment [Line Items]
Issued for services (shares) | shares						318,750
Proceeds from stock						$ 2,300
Cash paid for income taxes						400
Milestone payments						$ 2,700
Poziotinib [Member] | Licensing Agreements [Member]
Long-term Purchase Commitment [Line Items]
Potential payment based on achievement of regulatory milestones																						325,000
Zevalin Rights [Member]
Long-term Purchase Commitment [Line Items]
Payments receivable on achievement of potential sales milestones																					$ 2,000	2,000
Zevalin Rights [Member] | Total Consideration [Member]
Long-term Purchase Commitment [Line Items]
Total consideration received																	$ 18,000
Milestone net sales achievement							$ 3,000												$ 15,000			1,200	1,800
Zevalin Rights [Member] | Payment One [Member]
Long-term Purchase Commitment [Line Items]
Total consideration received								$ 15,000
Zevalin Rights [Member] | Payment Two [Member]
Long-term Purchase Commitment [Line Items]
Total consideration received							$ 3,000
Milestone net sales achievement																						1,200	$ 1,800
ZEVALIN, FOLOTYN, BELEODAQ, And MARQIBO [Member]
Long-term Purchase Commitment [Line Items]
Total consideration received	$ 6,000																	$ 6,000
Payment receivable on achievement of regulatory milestones																						$ 2,000
INDIA [Member] | ZEVALIN [Member] | Licensing Agreements [Member]
Long-term Purchase Commitment [Line Items]
Term										15 years
Recognition period																						10 years