Segment Information - Reconciliation of U.S. GAAP Income Before Income Taxes to Adjusted EBITDA (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Segment Reporting [Abstract]
Adjusted EBITDA		$ 23,984	$ 29,550
Stock-based compensation expense		(1,212)	(216)
Interest expense		(270)	(16)
Interest income and other	[1]	(201)	1,255
Depreciation and amortization		(5,194)	(3,543)
Income before income taxes		$ 17,107	$ 27,030

[1] Includes an impairment charge for royalty contracts resulting in $0.2 million and $0.9 million of expense for the three months ended March 31, 2019 and 2018, respectively. Includes a non-recurring adjustment for a change in estimated legal expenses resulting in $2.0 million of income for the three months ended March 31, 2018