Revenue - Changes in contract assets and contract liabilities (Details) $ in Thousands |
12 Months Ended |
|---|---|
|
Dec. 31, 2018
USD ($)
| |
| Contract assets | |
| Transferred to receivables from contract assets recognized at the beginning of the period | $ (353) |
| Net change in contract assets | (353) |
| Contract liabilities | |
| Revenue recognized that was included in the contract liability balance as of the beginning of the period | (10,783) |
| Increases due to cash received, net of amounts recognized as revenue during the period | 16,088 |
| Net change in contract liabilities | $ 5,305 |