Revenue from Contracts with Customers - Schedule of Comparison Between Reported Statements to Pro-forma Amounts in Effect of Previous Guidance - Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounts receivable, net	$ 520,381		$ 567,873
Contract assets	71,745		0
Prepaid expenses and other current assets	131,826		115,463
Contract assets - long-term	52,555		0
Deferred revenue, current	506,568		546,830
Deferred taxes, net	124,294
Accumulated deficit	(251,363)		$ (338,150)
ASC 606
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounts receivable, net		$ 535,925
Contract assets		90,449
Prepaid expenses and other current assets		127,109
Deferred revenue, current		533,929
Accumulated deficit		(276,770)
ASC 606 | Adjustments Due to ASC 606 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounts receivable, net	52,523	(31,948)
Contract assets	(71,745)	90,449
Prepaid expenses and other current assets	(13,184)	11,646
Contract assets - long-term	(52,555)
Deferred revenue, current	21,522	(12,901)
Deferred taxes, net	(27,816)
Accumulated deficit	(78,667)	$ 61,380
Pro forma Under ASC 605 [Member] | ASC 606
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounts receivable, net	572,904
Contract assets	0
Prepaid expenses and other current assets	118,642
Contract assets - long-term	0
Deferred revenue, current	528,090
Deferred taxes, net	96,478
Accumulated deficit	$ (330,030)