Revenue Recognition - Summary of Opening and Closing Balances of Contract Asset Contract Liability and Receivables (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Disaggregation Of Revenue [Line Items]
Accounts Receivable, Beginning Balance	$ 135,499
Accounts Receivable, Closing Balance	139,863
ASU 2014-09 [Member]
Disaggregation Of Revenue [Line Items]
Deferred Revenue (Current), Beginning Balance	2,189
Deferred Revenue (Current), Closing Balance	4,167
Deferred Revenue (Current), Increase/(Decrease)	1,978
Accounts Receivable, Beginning Balance	135,499
Accounts Receivable, Closing Balance	139,863
Accounts Receivable, Increase/(Decrease)	$ 4,364