| Earnings (loss) per share - Reconciliation of Earnings per share (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
| Jun. 30, 2016 | Jun. 30, 2015 | Jun. 30, 2016 | Jun. 30, 2015 | |
| Numerator for basic and diluted EPS | ||||
| Net loss | $ (22,095) | $ (14,568) | $ (37,671) | $ (16,513) | 
| Deemed dividend on convertible preferred shares | (2,229) | (8,663) | ||
| Net loss available to ordinary shareholders | $ (22,095) | $ (16,797) | $ (37,671) | $ (25,176) | 
| Denominator for basic and diluted EPS | ||||
| Weighted average number of shares used to calculate basic and diluted loss per share (in shares) | 424,711,900 | 316,559,989 | 424,711,900 | 248,222,243 | 
| X | ||||||||||
| 
- References No definition available. 
 | 
| X | ||||||||||
| 
- References No definition available. 
 | 
| X | ||||||||||
| 
- Definition The portion of profit or loss for the period, net of income taxes, which is attributable to the parent. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
 | 
| X | ||||||||||
| 
- Definition Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period). Reference 1: http://www.xbrl.org/2003/role/presentationRef 
 | 
| X | ||||||||||
| 
- Definition Amount of preferred stock dividends and adjustments classified as other. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
 | 
| X | ||||||||||
| 
- Definition Average number of shares or units issued and outstanding that are used in calculating basic and diluted earnings per share (EPS). No definition available. 
 |