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Revenue - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands | 9 Months Ended |
--- | --- | ---
Sep. 30, 2019 | Sep. 30, 2018 | Dec. 31, 2018
Capitalized Contract Cost [Line Items] |  |  |
Costs in excess of billings | $ 24,951 |  | $ 22,634
Amounts included in billings in excess of cost at the beginning of the period | 14,137 | $ 9,294 |
Amounts included in unearned revenue at the beginning of the period | 11,052 | $ 2,977 |
Billings in excess of cost |  |  |
Capitalized Contract Cost [Line Items] |  |  |
Contract with customer liability | (38,672) |  | (17,857)
Unearned revenue |  |  |
Capitalized Contract Cost [Line Items] |  |  |
Contract with customer liability | $ (21,860) |  | $ (12,028)

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- Definition Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130549-203045 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=118944033&loc=SL49130531-203044 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=118944033&loc=SL49130533-203044 + Details
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