Financial instruments - Fair Value of Significant Unobservable Inputs (Detail) - Significant Unobservable Inputs (Level 3) [Member] - Common Stock Warrants [Member] - Derivative Financial Instruments, Liabilities [Member] $ in Thousands |
3 Months Ended |
---|---|
Mar. 31, 2016
USD ($)
| |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | |
Beginning balance | $ 124 |
Change in fair value of derivative liabilities | (50) |
Ending balance | $ 74 |