Basis of Presentation - Additional Information (Detail) - USD ($) $ in Billions	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Feb. 29, 2016
Organization And Summary Of Significant Accounting Policies [Line Items]
Total backlog	$ 2.5
Percentage of revenue expected to be recognized over next 12 months	59.00%
ASU No. 2016-02
Organization And Summary Of Significant Accounting Policies [Line Items]
New accounting pronouncement or change in accounting principle effect of additional assets and liabilities			$ 1.2
Receivables Less Allowance for Doubtful Accounts
Organization And Summary Of Significant Accounting Policies [Line Items]
Revenue in excess of billings	$ 0.2	$ 0.3
Accounts Payable and Accrued Liabilities
Organization And Summary Of Significant Accounting Policies [Line Items]
Billings and cash collections in excess of revenue	$ 0.8	$ 0.8
Minimum
Organization And Summary Of Significant Accounting Policies [Line Items]
Revenue recognition period	30 days
Maximum
Organization And Summary Of Significant Accounting Policies [Line Items]
Revenue recognition period	60 days