Revenue - Summary of Asset Balances and Related Amortization Expense For Contract Costs (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Costs to Obtain a Contract [Member]
Capitalized Contract Cost [Line Items]
Beginning Balance	$ 178,445	$ 140,119	$ 158,989	$ 126,207
Capitalization of Costs	11,315	10,595	42,513	33,565
Amortization	(6,321)	(4,855)	(18,063)	(13,913)
Ending Balance	183,439	145,859	183,439	145,859
Costs to Fulfill a Contract [Member]
Capitalized Contract Cost [Line Items]
Beginning Balance	121,664	87,199	101,756	72,061
Capitalization of Costs	15,323	9,730	42,614	30,156
Amortization	(4,258)	(3,001)	(11,641)	(8,289)
Ending Balance	$ 132,729	$ 93,928	$ 132,729	$ 93,928