Fair value of financial instruments - Summary of Fair Value of Financial Liabilities (Details) - Fair Value Measurements, Recurring Basis - USD ($) $ in Thousands |
Dec. 31, 2017 |
Dec. 31, 2016 |
---|---|---|
Financial liabilities: | ||
Long-term debt, including current portion | $ 156,792 | $ 165,393 |
Total financial liabilities | 156,792 | 165,393 |
Current portion of long-term debt | 8,646 | 8,650 |
Level 1 | ||
Financial liabilities: | ||
Long-term debt, including current portion | 0 | 0 |
Total financial liabilities | 0 | 0 |
Level 2 | ||
Financial liabilities: | ||
Long-term debt, including current portion | 156,792 | 165,393 |
Total financial liabilities | 156,792 | 165,393 |
Level 3 | ||
Financial liabilities: | ||
Long-term debt, including current portion | 0 | 0 |
Total financial liabilities | $ 0 | $ 0 |