Revenue - Significant Changes in Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Change In Contract With Customer, Asset [Roll Forward]
Contract assets balance, beginning of year	$ 4,083	$ 6,278
Transferred to receivables	(8,371)	(8,865)
Additional unbilled receivables	5,378	6,670
Contract assets balance, end of period	1,090	4,083
Change In Contract With Customer, Liability [Roll Forward]
Contract liabilities balance, beginning of year	42,809	56,426
Revenue recognized	(10,901)	(13,493)
Increases (decreases) due to cash received, excluding amounts recognized as revenue during the period	774	(124)
Contract liabilities balance, end of period	$ 32,682	$ 42,809

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 (Decrease) 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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-Publisher FASB
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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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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.

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

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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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