Fair Value Measurements (Narrative) (Detail) $ / shares in Units, shares in Millions				3 Months Ended			6 Months Ended			12 Months Ended
		Aug. 02, 2018 USD ($)	Jul. 08, 2016 USD ($)	Jun. 30, 2019 USD ($)		Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)		Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)		Aug. 03, 2018 USD ($)	Jun. 29, 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 ($)	Oct. 18, 2013 USD ($)
Intangible Assets, Net (Excluding Goodwill)	[1]			$ 50,449,000			$ 50,449,000			$ 51,319,000
Impairment of Intangible Assets, Finite-lived				0		$ 152,330,000	0		$ 152,330,000	152,300,000
Investment Owned, at Cost				$ 6,600,000			6,600,000
Goodwill and Intangible Asset Impairment							$ 152,300,000
Cash payment for purchase of royalty right																		$ 65,600,000
Purchase of royalty rights		$ 20,000,000
Reversionary interest period												$ 481,000,000
Sensitivity range for royalty disclosures				2.50%			2.50%
Royalty rights				$ 315,642,000	[1]		$ 315,642,000	[1]		376,510,000	[2]
Transfers from level 1 to level 2, amount				0			0			0
Transfers from level 2 to level 1, amount				0			0			0
Percentage of royalty acquired																		75.00%
Revenues				(22,526,000)		46,575,000	16,387,000		85,093,000
Finite-Lived Intangible Assets, Gross				58,052,000			58,052,000			55,752,000
Asset Impairment Charges				$ 0			0			$ 8,200,000
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
Sensitivity - decrease in fair value from increase in discount rate				$ 22,200,000			22,200,000
Sensitivity - increase in fair value from decrease in discount rate				26,300,000			26,300,000
Sensitivity to increase or decrease in expected royalty				6,600,000			6,600,000
Royalty rights				263,900,000			263,900,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount				$ 263,900,000			$ 263,900,000
Contractual cap on potential royalty asset multiple							2
VB [Member]
Purchase of royalty rights																			$ 15,500,000
Cash flow model expected royalty sales term				9 years
Sensitivity - decrease in fair value from increase in discount rate				$ 1,300,000			$ 1,300,000
Sensitivity - increase in fair value from decrease in discount rate				1,500,000			1,500,000
Sensitivity to increase or decrease in expected royalty				$ 400,000			$ 400,000
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate				15.00%			15.00%
Royalty rights				$ 14,400,000			$ 14,400,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount				$ 14,400,000			$ 14,400,000
Contractual cap on potential royalty asset multiple							2.3
University of Michigan [Member]
Cash flow model expected royalty sales term				3 years
Sensitivity - decrease in fair value from increase in discount rate				$ 900,000			$ 900,000
Sensitivity - increase in fair value from decrease in discount rate				1,000,000			1,000,000
Sensitivity to increase or decrease in expected royalty				$ 600,000			$ 600,000
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate				12.80%			12.80%
Royalty rights				$ 24,300,000			$ 24,300,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount				$ 24,300,000			24,300,000
AcelRx [Member]
Purchase of royalty rights																	$ 65,000,000
Cash flow model expected royalty sales term				14 years
Sensitivity - decrease in fair value from increase in discount rate				$ 1,200,000			1,200,000
Sensitivity - increase in fair value from decrease in discount rate				1,500,000			1,500,000
Sensitivity to increase or decrease in expected royalty				$ 300,000			$ 300,000
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate				13.40%			13.40%
Royalty rights				$ 12,500,000			$ 12,500,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount				12,500,000			$ 12,500,000
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
Revenues				$ 60,000,000
Kybella [Member]
Purchase of royalty rights														$ 9,500,000
Cash flow model expected royalty sales term				6 years
Sensitivity - increase in fair value from decrease in discount rate				$ 100,000			$ 100,000
Sensitivity to increase or decrease in expected royalty				$ 100,000			$ 100,000
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate				14.40%			14.40%
Royalty rights				$ 600,000			$ 600,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount				$ 600,000			$ 600,000
Maximum amount of additional funds, upon attainment of milestones			$ 1,000,000
Alphaeon [Member]
Investment Owned, Balance, Shares | shares																1.7
Investment estimated fair value, per share | $ / shares															$ 3.84
Noden [Member]
Intangible Assets, Net (Excluding Goodwill)						40,100,000			40,100,000
Finite-Lived Intangible Assets, Gross						$ 40,100,000			$ 40,100,000				$ 192,500,000
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%

[1] unaudited

[2] Note 1