Intangible assets - Rollforward (Details) - USD ($) $ in Thousands |
1 Months Ended | 12 Months Ended | ||
|---|---|---|---|---|
Jan. 31, 2017 |
Nov. 30, 2016 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Changes in intangible assets | ||||
| Balance at beginning of year | $ 13,783 | $ 16,055 | $ 19,676 | |
| Additions | 1,210 | |||
| Amortization expense | (3,470) | (3,594) | ||
| Impairment loss | (12) | (27) | ||
| Balance at end of year | $ 13,783 | $ 16,055 | ||
| Caching technology intangible | ||||
| Changes in intangible assets | ||||
| Additions | $ 1,210 | |||
| Acquisition cost of intangible asset | $ 1,250 | |||
| Payment of the purchase price | $ 1,150 | |||
| Estimated useful life (in years) | 4 years | |||
| Caching technology intangible | Cost savings and replacement cost methods | ||||
| Changes in intangible assets | ||||
| Discount rate (as a percent) | 20.00% | |||