Fair Value Measurements - Roll-Forward of Fair Value of Derivative Liability (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value of derivative liability, recorded as interest expense	$ 283	$ (96)	$ 2,238
Probability-Weighted Discounted Cash Flow Model [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Balance at December 31, 2018	2,142
Change in fair value of derivative liability, recorded as interest expense	283
Balance at December 31, 2019	$ 2,425	$ 2,142