Summary of Changes in Estimated Fair Value of Embedded Derivatives Liabilities Measured on Recurring Basis (Detail) - Embedded derivative liabilities $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance as of December 31, 2016	$ 246
Issuance of embedded derivatives	609
Net increase in fair value included in other income (expense)	666
Balance as of June 30, 2017	$ 1,521