Annual Depreciation Rates of Property, Plant and Equipment (Detail)	12 Months Ended
	Dec. 31, 2017
Computers, software and equipment | Minimum
Property, Plant and Equipment [Line Items]
Annual depreciation rate	10.00%
Computers, software and equipment | Maximum
Property, Plant and Equipment [Line Items]
Annual depreciation rate	33.00%
Office furniture and equipment | Minimum
Property, Plant and Equipment [Line Items]
Annual depreciation rate	7.00%
Office furniture and equipment | Maximum
Property, Plant and Equipment [Line Items]
Annual depreciation rate	33.00%
Leasehold improvements
Property, Plant and Equipment [Line Items]
Annual depreciation rate	(the shorter of the expected lease term or useful economic life)
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Annual depreciation rate	10.00%
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Annual depreciation rate	25.00%