Revenue - Receivables and Concentration of Credit Risk (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable, Net, Current [Abstract]
Billed Receivables	$ 175,066	$ 240,137
Allowance for doubtful accounts	(4,001)	(4,799)
Billed Receivables, net	171,065	235,338
Accrued receivables	328,546	27,507
Significant financing component	(34,109)
Total accrued receivables, net	294,437	27,507
Less current accrued receivables	117,276	27,507
Less current significant financing component	(9,972)
Total long-term accrued receivables, net	187,133
Total receivables, net	$ 465,502	$ 262,845