Fair Value of Financial Assets and Liabilities - Summary of Changes in Fair Value of Derivative Liability for Fair Value Determined by Level 3 Inputs (Detail) - Level 3 [Member] - Derivative Liabilities [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 371	$ 88
Change in fair value	1,629	283
Payment	$ (2,000)
Ending balance		$ 371