Short-Term Investments - Summary of Short-Term Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 26, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 55,168	$ 80,212
Gross Unrealized Gains	31	62
Gross Unrealized Losses	(48)	(22)
Total short-term investments, Estimated Fair Value	55,151	80,252
State, municipal and local government agencies bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	25,719	40,426
Gross Unrealized Gains	26	38
Gross Unrealized Losses	(31)	(15)
Total short-term investments, Estimated Fair Value	25,714	40,449
Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	26,150	33,483
Gross Unrealized Gains	5	20
Gross Unrealized Losses	(17)	(7)
Total short-term investments, Estimated Fair Value	26,138	33,496
Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	3,299	2,299
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Total short-term investments, Estimated Fair Value	3,299	2,299
U.S. federal government bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	0	4,004
Gross Unrealized Gains	0	4
Gross Unrealized Losses	0	0
Total short-term investments, Estimated Fair Value	$ 0	$ 4,008