Revenue from Contracts with Customers - Impact of Adoption on Previously Reported Condensed Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	$ 520,381		$ 567,873
Contract assets	71,745		0
Prepaid expenses and other current assets	131,826		115,463
Deferred revenue, current	506,568		546,830
Deferred revenue, long-term			24,047
Deferred taxes, net	124,294		93,643
Accumulated deficit	(251,363)		$ (338,150)
ASC 606
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net		$ 535,925
Contract assets		90,449
Prepaid expenses and other current assets		127,109
Deferred revenue, current		533,929
Deferred revenue, long-term		24,047
Deferred taxes, net		115,311
Accumulated deficit		(276,770)
ASC 606 | Adjustments Due to ASC 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [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
Deferred revenue, current	21,522	(12,901)
Deferred revenue, long-term		0
Deferred taxes, net		21,668
Accumulated deficit	$ (78,667)	$ 61,380