Fair Value Measurements (Narrative) (Detail) $ / shares in Units, shares in Millions			2 Months Ended	3 Months Ended		8 Months Ended	9 Months Ended
	Aug. 02, 2018 USD ($)	Jul. 08, 2016 USD ($)	Aug. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Aug. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) numberOfNotesRecivables	Aug. 03, 2018 USD ($)	Jul. 09, 2016 USD ($)	Dec. 31, 2015 $ / shares	Dec. 15, 2015 shares	Sep. 18, 2015 USD ($)	Nov. 06, 2014 USD ($)	Jun. 26, 2014 USD ($)	Oct. 18, 2013 USD ($)
Financing Receivable, before Allowance for Credit Loss, Noncurrent											$ 52,100,000
Cash payment for purchase of royalty right																	$ 65,600,000
Purchase of royalty rights	$ 20,000,000.0
Proceeds from the sale of intangible assets							$ 0	$ 5,000,000
Gain on sale of intangible assets			$ 0		$ 3,476,000	$ 0		3,476,000
Reversionary interest period												$ 481,000,000.0
Number of notes receivable assets | numberOfNotesRecivables											2
Percentage of royalty acquired																	75.00%
Convertible Notes Payable, Carrying Value				$ 15,238,000			$ 15,238,000				$ 27,250,000
Notes Payable, Fair Value Disclosure											33,900,000
Depomed [Member]
Cash payment for purchase of royalty right																			$ 240,500,000
Purchase of royalty rights																			241,300,000
Royalty right purchase transaction costs																			$ 800,000
Cash flow model expected royalty sales term			8 years
Contractual cap on potential royalty asset multiple							2
VB [Member]
Purchase of royalty rights																		$ 15,500,000
Proceeds from the sale of intangible assets				4,200,000
Gain on sale of intangible assets				0
Contractual cap on potential royalty asset multiple							2.3
University of Michigan
Cash flow model expected royalty sales term			2 years
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate			12.80%			12.80%
AcelRx [Member]
Purchase of royalty rights																$ 65,000,000.0
Period to give notice to terminate license agreement							180 days
Proceeds from the sale of intangible assets				0
Gain on sale of intangible assets						$ 0
Percentage of royalty acquired																75.00%
Percentage of first four milestone payments acquired																80.00%
Number of potential milestone royalties																4
Contractual cap on potential royalty asset multiple							3
Kybella [Member]
Purchase of royalty rights													$ 9,500,000
Proceeds from the sale of intangible assets				200,000
Gain on sale of intangible assets				$ 0
Maximum amount of additional funds, upon attainment of milestones		$ 1,000,000.0
Alphaeon [Member]
Investment Owned, Balance, Shares | shares															1.7
Investment Owned, at Cost			$ 1,000,000.0			$ 1,000,000.0					6,600,000
Investment estimated fair value, per share | $ / shares														$ 3.84
Minimum [Member] | Depomed [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate			10.00%			10.00%
Maximum [Member] | Depomed [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate			24.00%			24.00%
Discontinued Operations, Held-for-sale
Loss on classification as held for sale			$ 0		$ 0	$ (28,904,000)		$ 0
Royalty rights											266,196,000
Discontinued Operations, Held-for-sale | Income generating assets [Member]
Loss on classification as held for sale			$ 4,600,000			$ 4,600,000
Discontinued Operations, Held-for-sale | Pharmaceutical [Member]
Estimated cost to sell										$ 1,800,000
Loss on classification as held for sale, fair value adjustment										4,900,000
Loss on classification as held for sale									$ 16,800,000	$ 6,700,000
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate									17.00%	19.00%
Fair Value Level 3 [Member]
Royalty rights											266,196,000
Notes Receivable, Fair Value Disclosure											$ 57,300,000