Revenue Recognition (Details 2) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Contract assets:
Current portion of contract assets	$ 18,798	$ 18,248	$ 0
Contract assets	3,566	3,566	0
Total contract assets	22,364		0
Advances on contracts:
Current portion of advances on contracts	39,559	39,451	117,958
Advances on contracts	13,493	$ 24,564	0
Total advances on contracts	$ 53,052		$ 117,958

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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