Fair Value Measurements (Financial Instruments Measured at Fair Value on a Recurring Basis) (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Financial assets:
Assets, Fair Value	$ 321,592	$ 493,879
Warrants and Rights Outstanding	5,431	14,152
Equity Securities [Member]
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in and Advances to Affiliates, at Fair Value	0	82,267
Money Market Funds [Member]
Financial assets:
Cash and Cash Equivalents, Fair Value	81,919	131,264
Fair Value Level 1 [Member]
Financial assets:
Assets, Fair Value	81,919	213,531
Fair Value Level 1 [Member] | Equity Securities [Member]
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in and Advances to Affiliates, at Fair Value	0	82,267
Fair Value Level 1 [Member] | Money Market Funds [Member]
Financial assets:
Cash and Cash Equivalents, Fair Value	81,919	131,264
Fair Value Level 2 [Member]
Financial assets:
Assets, Fair Value	5,431	14,152
Warrants and Rights Outstanding	5,431	14,152
Fair Value Level 2 [Member] | Equity Securities [Member]
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in and Advances to Affiliates, at Fair Value	0	0
Fair Value Level 2 [Member] | Money Market Funds [Member]
Financial assets:
Cash and Cash Equivalents, Fair Value	0	0
Fair Value Level 3 [Member]
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Royalty rights	234,242	266,196
Financial assets:
Assets, Fair Value	234,242	$ 266,196
Warrants and Rights Outstanding	0
Royalty right [Member]
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	(31,954)
VB [Member]
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Royalty rights	4,300
VB [Member] | Royalty right [Member]
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	$ (9,199)