Percentage of Revenue by Geographic Area (Detail) - Geographic Concentration Risk - Total Revenue	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Concentration Risk [Line Items]
Revenues, percentage by country	100.00%	100.00%	100.00%	100.00%
North America
Concentration Risk [Line Items]
Revenues, percentage by country	49.00%	45.00%	47.00%	40.00%
Europe
Concentration Risk [Line Items]
Revenues, percentage by country	39.00%	45.00%	41.00%	50.00%
Asia and Australia
Concentration Risk [Line Items]
Revenues, percentage by country	12.00%	10.00%	12.00%	10.00%
Other
Concentration Risk [Line Items]
Revenues, percentage by country	0.00%	0.00%	0.00%	0.00%