Inventories - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 26, 2015	Sep. 26, 2015	Sep. 27, 2014	Dec. 31, 2014
Inventory [Line Items]
Demonstration inventory shelf life		3 years
Refurbished demonstration inventory selling period		12 months
Inventories, net	$ 55,110	$ 55,110		$ 43,094
Fixed assets, useful life		3 years
Write-down of inventories		$ 9,560	$ 3,588
Finished goods
Inventory [Line Items]
Demonstration inventory				3,000
Excess Inventory
Inventory [Line Items]
Write-down of inventories	5,900
Purchase Commitment Inventory
Inventory [Line Items]
Write-down of inventories	2,000
Excess Inventory and Purchase Commitment Inventory
Inventory [Line Items]
Write-down of inventories		7,900
Service and demonstration inventory, net | Demonstration inventory
Inventory [Line Items]
Inventories, net	18,000	18,000		$ 16,200
Property and equipment
Inventory [Line Items]
Service inventory	$ 3,000	$ 3,000