Fair Value Measurements (Narrative) (Detail) - USD ($) $ / shares in Units, shares in Millions						3 Months Ended		12 Months Ended
	Jan. 07, 2018	Dec. 13, 2016	Sep. 21, 2016	Jul. 08, 2016	Jun. 02, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Aug. 01, 2018	Jun. 30, 2018	Jun. 27, 2018	Mar. 29, 2017	Jul. 09, 2016	Dec. 15, 2015	Sep. 18, 2015	Jul. 28, 2015	Nov. 06, 2014	Jun. 26, 2014	Oct. 18, 2013
Investment Owned, Balance, Shares																1.7
Asset Impairment Charges								$ 8,200,000	$ 0	$ 3,735,000
Investment estimated fair value, per share						$ 3.84		$ 3.84
Impairment of Intangible Assets, Finite-lived								$ 152,330,000	0	0
Intangible assets, net						$ 51,319,000	$ 215,823,000	51,319,000	215,823,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value						376,510,000	349,223,000	376,510,000	349,223,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings								7,287,000
Cash payment for purchase of royalty right																			$ 65,600,000
Proceeds from Sale of Productive Assets								0	108,169,000	0
Sale of royalty multiple														120.00%
Proceeds from Legal Settlements							13,000,000
Royalty rights - at fair value						376,510,000	349,223,000	376,510,000	349,223,000
Percentage of royalty acquired																			75.00%
Revenue Recognition, Milestone Method, Revenue Recognized		$ 6,000,000	$ 5,000,000		$ 6,000,000
Maximum amount of additional funds, upon attainment of milestones	$ 2,000,000
Change in fair value of acquired royalty rights, Level 3 Rollforward								85,256,000	162,327,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings								41,631,000	(349,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements								(858,000)	0	$ 0
Notes Receivable, Fair Value Disclosure						70,000,000	71,300,000	70,000,000	71,300,000
Investment Owned, at Fair Value																$ 6,600,000
Transfers from level 1 to level 2, amount						0	0	0	0
Transfers from level 2 to level 1, amount						$ 0	0	$ 0	0
VB [Member]
Cash flow model expected royalty sales term						10 years
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate						15.00%		15.00%
Fair Value Measurements, Sensitivity Analysis, Description								Should this discount rate increase or decrease by 2.5%, the fair value of this asset could decrease by $1.4 million or increase by $1.6 million, respectively. Should the expected royalties increase or decrease by 2.5%, the fair value of the asset could increase or decrease by $0.4 million, respectively.
Royalty rights - at fair value						$ 14,100,000		$ 14,100,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount						$ 14,100,000		$ 14,100,000												$ 15,500,000
Royalty asset multiple								0
University of Michigan [Member]
Cash flow model expected royalty sales term						4 years
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate						12.80%		12.80%
Fair Value Measurements, Sensitivity Analysis, Description								Should this discount rate increase or decrease by 2.5%, the fair value of this asset could decrease by $1.1 million or increase by $1.2 million, respectively. Should the expected royalties increase or decrease by 2.5%, the fair value of the asset could increase or decrease by $0.6 million, respectively.
Royalty rights - at fair value						$ 25,600,000		$ 25,600,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount						$ 25,600,000		$ 25,600,000
Depomed [Member]
Cash payment for purchase of royalty right											$ 20,000,000										$ 240,500,000
Maximum royalty prior to amendment																					481,000,000
Cash flow model expected royalty sales term						9 years
Purchase of royalty right																					241,300,000
Royalty right purchase transaction costs																					$ 800,000
Fair Value Measurements, Sensitivity Analysis, Description								Should these discount rates increase or decrease by 2.5%, the fair value of the asset could decrease by $22.9 million or increase by $27.2 million, respectively. A third-party expert was engaged to assist management develop its original estimate of the expected future cash flows, which was updated after the acquisition of Depomed’s reversionary interest in August 2018. The estimated fair value of the asset is subject to variation should those cash flows vary significantly from those estimates. The Company periodically assesses the expected future cash flows and to the extent such payments are greater or less than its initial estimates, or the timing of such payments is materially different than the original estimates, the Company will adjust the estimated fair value of the asset. Should the expected royalties increase or decrease by 2.5%, the fair value of the asset could increase or decrease by $6.6 million, respectively.
Royalty rights - at fair value						$ 264,400,000		$ 264,400,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount						$ 264,400,000		$ 264,400,000
ARIAD [Member]
Proceeds from Sale of Productive Assets									108,200,000
Purchase of royalty right																		$ 100,000,000
Royalty Guarantees, Commitments, Amount																		200,000,000
ARIAD [Member] | Tranche 1 [Member]
Purchase of royalty right																		50,000,000
ARIAD [Member] | Tranche 3 [Member]
Cash payment for purchase of royalty right																		$ 100,000,000
AcelRx [Member]
Cash flow model expected royalty sales term						14 years
Purchase of royalty right																	$ 65,000,000
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate						13.40%		13.40%
Fair Value Measurements, Sensitivity Analysis, Description								Should this discount rate increase or decrease by 2.5%, the fair value of this asset could decrease by $9.9 million or increase by $12.2 million, respectively. Should the expected royalties increase or decrease by 2.5%, the fair value of the asset could increase or decrease by $1.8 million, respectively.
Royalty rights - at fair value						$ 70,400,000		$ 70,400,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount						$ 70,400,000		$ 70,400,000
Percentage of royalty acquired																	75.00%
Kybella [Member]
Cash flow model expected royalty sales term						7 years
Purchase of royalty right															$ 9,500,000
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate						14.40%		14.40%
Fair Value Measurements, Sensitivity Analysis, Description								Should this discount rate increase or decrease by 2.5%, the fair value of this asset could decrease or increase by $0.2 million, respectively. Should the expected royalties increase or decrease by 2.5%, the fair value of the asset could increase or decrease by $0.1 million, respectively.
Royalty rights - at fair value						$ 2,100,000		$ 2,100,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount						$ 2,100,000		$ 2,100,000
Maximum amount of additional funds, upon attainment of milestones				$ 1,000,000
Alphaeon [Member]
Investment Owned, Balance, Shares						1.7		1.7
Investment Owned, at Fair Value						$ 6,600,000	6,600,000	$ 6,600,000	6,600,000
Contingent Consideration [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value						$ (1,071,000)	$ (42,000,000)	(1,071,000)	$ (42,000,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases								1,560,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings								41,631,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements								858,000
Noden [Member]
Impairment of Intangible Assets, Finite-lived								152,300,000
Intangible assets, net												$ 40,100,000	$ 192,500,000
CareView [Member]
Asset Impairment Charges								$ 8,200,000
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%