Fair Value Measurements - Schedule of Reconciliation of Debt Security and Warrant (Detail) - eNeura Inc [Member] - Debt Security and Warrant [Member] - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 17,820	$ 16,050
Gains or losses recorded for the period
Recognized in other comprehensive income (loss)	(2,593)	1,960
Change in classification of debt security to held to maturity	(15,227)	0
Issuance of warrant as consideration for extension	491	0
Ending balance	$ 491	$ 18,010