Reclassifications Out of Accumulated Other Comprehensive (Loss) Income to Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2017	Jul. 03, 2016	Jul. 02, 2017	Jul. 03, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	$ (3,292)	$ (1,666)	$ (6,812)	$ (3,308)
Reclassifications, net of tax			313	297
Unrealized Gains (Losses) on Marketable Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, net of tax			177	134
Amortization of prior service credit
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, net of tax	68	83	136	163
Accumulated Other Comprehensive Income (Loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, net of tax	151	134	313	297
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Gains (Losses) on Marketable Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	$ 83	$ 51	$ 177	$ 134