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 |
12 Months Ended |
---|---|
Dec. 31, 2015
USD ($)
| |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | |
Beginning balance | $ 72 |
Change in fair value of derivative liabilities | 52 |
Ending balance | $ 124 |