Schedule of Company's Obligations Under Acquisitions and Licensing Agreements (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Combinations [Abstract]
Beginning Balance	$ 815	$ 1,535	$ 2,492
Additional obligations acquired	10,992	224	1,367
Adjustment to deferred liabilities	(223)	(22)	65
Amortization of discounted liabilities	109	38	135
Payments on existing obligations	(26)	(960)	(2,524)
Ending Balance	$ 11,667	$ 815	$ 1,535