Revenue - Receivables and Concentration of Credit Risk (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable, Net, Current [Abstract]
Billed receivables	$ 239,275	$ 240,137
Allowance for doubtful accounts	(3,912)	(4,799)	$ (3,873)	$ (5,045)
Billed receivables, net	235,363	235,338
Accrued receivables	336,858	27,507
Significant financing component	(35,029)
Total accrued receivables, net	301,829	27,507
Less current accrued receivables	123,053	27,507
Less current significant financing component	(10,234)
Total long-term accrued receivables, net	189,010
Total receivables, net	$ 537,192	$ 262,845

Amount, after accumulated amortization, of the financing component related to unbilled receivable balances.

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Amount, after accumulated amortization, of the financing component related to unbilled receivable balances due within one year of the balance sheet date.

+ References

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Amount received for services rendered and products shipped, but not yet billed, for non-contractual agreements net of the significant financing component.

+ References

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Amounts due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer) for goods or services (including trade receivables) that have been delivered or sold in the normal course of business.

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For an unclassified balance sheet, the amount due from customers or clients for goods or services that have been delivered or sold in the normal course of business, reduced to their estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

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Amount due from customers or clients, more than one year from the balance sheet date, for goods or services that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

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A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

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The total amount due to the entity within one year of the balance sheet date (or one operating cycle, if longer) from outside sources, including trade accounts receivable, notes and loans receivable, as well as any other types of receivables, net of allowances established for the purpose of reducing such receivables to an amount that approximates their net realizable value.

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Unbilled amounts due for services rendered or to be rendered, actions taken or to be taken, or a promise to refrain from taking certain actions in accordance with the terms of a legally binding agreement between the entity and, at a minimum, one other party. An example would be amounts associated with contracts or programs where the recognized revenue for performance thereunder exceeds the amounts billed under the terms thereof as of the date of the balance sheet.

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Amount received for services rendered and products shipped, but not yet billed, for non-contractual agreements due within one year or the normal operating cycle, if longer.

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