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
	Oct. 03, 2018	Nov. 30, 2018 USD ($)	Apr. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Aug. 31, 2017 USD ($)	Jul. 31, 2017 USD ($) shares	Jun. 30, 2017 USD ($)	Apr. 30, 2016 USD ($) shares	Mar. 31, 2016 USD ($)	Feb. 29, 2016	Jan. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Feb. 28, 2015 USD ($)	Jun. 30, 2014	Feb. 28, 2014 USD ($)	Apr. 30, 2012 EUR (€)	Feb. 28, 2010 USD ($)	Nov. 30, 2009 USD ($)	Oct. 31, 2008 USD ($) shares	Jan. 31, 2016 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2017 USD ($) shares	Dec. 31, 2018 USD ($) Country	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) shares	Jan. 01, 2019 USD ($)	Nov. 30, 2014 USD ($)	Jul. 17, 2013 USD ($)
Long-term Purchase Commitment [Line Items]
Rental expense																																	$ 1,600	$ 1,600	$ 1,500
Total revenues																					$ 29,402	$ 25,268	$ 24,168	$ 30,495	$ 28,570	$ 36,395	$ 34,301	$ 29,101					$ 109,333	128,367	$ 146,444
Payment of all royalty obligations				$ 2,600
Percentage of royalty on annual worldwide sales under condition one																					20.00%												20.00%
Intangible assets, gross																					$ 308,318				305,668							$ 305,668	$ 308,318	305,668
Additional license fees																																	$ 60,000
Percentage of royalties on net sale of licensed products																																	20.00%
Acquisition-related contingent obligations																					4,345				6,272							$ 6,272	$ 4,345	6,272
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	0	128,272	$ 73,869
Cash paid for income taxes																																	45	17	11
Deferred compensation liability, current																					6,200				11,000							11,000	6,200	11,000
Allergan [Member]
Long-term Purchase Commitment [Line Items]
Up-front non-refundable payment																			$ 41,500
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]
Potential milestone payments																																	16,000
Commercial progress and sales-dependent [Member] | Maximum [Member]
Long-term Purchase Commitment [Line Items]
Potential milestone payments																																	$ 107,000
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%
Potential payment based on achievement of regulatory milestones																																	$ 3,500
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
KHAPZORY [Member]
Long-term Purchase Commitment [Line Items]
Milestone payments		$ 2,700
BELEODAQ distribution rights [Member]
Long-term Purchase Commitment [Line Items]
Intangible assets, gross																					$ 25,000				25,000							25,000	25,000	25,000
Duration of automatic stay triggered upon ANDA	30 months
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																					4,300				$ 6,200							$ 6,200	4,300	6,200
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 sales milestones																																	325,000
Potential payment based on achievement of regulatory milestones																																	33,000
Zevalin Rights [Member] | Total Consideration [Member]
Long-term Purchase Commitment [Line Items]
Total consideration received																				$ 18,000
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
ZEVALIN, FOLOTYN, BELEODAQ, And MARQIBO [Member]
Long-term Purchase Commitment [Line Items]
Total consideration received		$ 1,000																											$ 6,000
Payment receivable on achievement of regulatory milestones																																	1,000
INDIA [Member] | ZEVALIN [Member] | Licensing Agreements [Member]
Long-term Purchase Commitment [Line Items]
Term														15 years
License and Service [Member]
Long-term Purchase Commitment [Line Items]
Total revenues																																	4,867	12,189	$ 17,848
License and Service [Member] | Regulatory [Member] | Maximum [Member]
Long-term Purchase Commitment [Line Items]
Total revenues					$ 3,000
License and Service [Member] | Zevalin Rights [Member]
Long-term Purchase Commitment [Line Items]
Total revenues			$ 2,000
License and Service [Member] | Zevalin Rights [Member] | Total Consideration [Member]
Long-term Purchase Commitment [Line Items]
Total revenues							$ 3,000																							$ 15,000
License and Service [Member] | ZEVALIN, FOLOTYN, BELEODAQ, And MARQIBO [Member]
Long-term Purchase Commitment [Line Items]
Total revenues																													$ 6,000
License [Member] | Allergan [Member]
Long-term Purchase Commitment [Line Items]
License costs																			$ 300
Ligand Pharmaceuticals Inc [Member]
Long-term Purchase Commitment [Line Items]
Milestone payments								$ 6,000	$ 6,000
Medac [Member] | KHAPZORY [Member]
Long-term Purchase Commitment [Line Items]
Milestone payments																																	2,700	$ 300
MD Anderson [Member]
Long-term Purchase Commitment [Line Items]
Potential payment based on achievement of sales milestones																																	23,000
Payment of all royalty obligations			$ 500
Potential payment based on achievement of regulatory milestones																																	11,000
Restatement Adjustment [Member] | Melphalan In Process Research and Development [Member]
Long-term Purchase Commitment [Line Items]
Intangible assets, gross																					$ (7,700)												$ (7,700)
Accounting Standards Update 2016-02 [Member] | Scenario, Forecast [Member]
Long-term Purchase Commitment [Line Items]
Right-of-use asset																																				$ 4,400
Lease liability																																				$ 4,400