v3.19.2

Contract assets and contract liabilities (Tables) | 6 Months Ended
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Jun. 30, 2019
Contract assets and contract liabilities |
Schedule of contract asset, net and contract liability, net balance from customers and performance obligations included in revenues | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Contract | ​ | Contract
​ |  | Assets, Net |  | Liabilities, Net
Balance at December 31, 2018 | ​ | $ | 468 | ​ | $ | 217,733
Balance at June 30, 2019 | ​ | ​ | 756 | ​ | ​ | 237,109
Change | ​ | $ | 288 | ​ | $ | 19,376
​ ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended | ​ | Six Months Ended
​ |  | June 30, 2019 |  | June 30, 2019
Amounts included in the beginning of period contract liability balance | ​ | $ | 22,629 | ​ | $ | 51,500
Amounts associated with performance obligations satisfied in previous periods | ​ |  | 7 | ​ | ​ | 301

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- Definition Tabular disclosure of contract balances and changes in contract balances. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130551-203045 + Details
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