Revenue Recognition - Contract Assets and Advances on Contracts (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Contract assets:
Current portion of contract assets	$ 17,478	$ 24,254
Total contract assets	17,500	24,300
Advances on contracts:
Current portion of advances on contracts	37,014	31,317
Advances on contracts	27,478	37,675
Total advances on contracts	64,500	$ 69,000
Contract with Customer, Liability, Revenue Recognized	$ 21,500

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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