Contract Assets and Contract Liabilities - Changes in Net Contract Assets (Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Contract assets, current	$ 679	$ 325
Contract assets, non-current	245	0
Contract assets	924	325
Contract liabilities, current	4,843	2,252
Contract liabilities, non-current	2,378	4,442
Contract liabilities	$ 7,221	$ 6,694

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 45
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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

+ References

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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as noncurrent.

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