Revenue - Significant Changes in Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Change In Contract With Customer, Asset [Roll Forward]
Balance, beginning of year	$ 6,278	$ 2,015
Transferred to receivables	(6,402)	(2,909)
Additional unbilled receivables	3,469	7,172
Balance, end of period	3,345	6,278
Change In Contract With Customer, Liability [Roll Forward]
Balance, beginning of year	56,426	62,232
Revenue recognized	(9,828)	(5,892)
Cash received	28	86
Balance, end of period	$ 46,626	$ 56,426

Change In Contract With Customer, Asset [Roll Forward]

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- Definition

Change In Contract With Customer, Liability [Roll Forward]

+ References

No definition available.

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- Definition

Contract With Customer, Liability, Increase From Cash Receipts

+ References

No definition available.

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- Definition

Amount of increase (decrease) in revenue recognized for cumulative catch-up adjustment from change in measure of progress which increases (decreases) right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

+ References

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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.

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- Definition

Amount of decrease in right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time from transfer to receivable due to right to consideration becoming unconditional.

+ References

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- Definition

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

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- Definition

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

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