Accumulated Other Comprehensive Loss (Details 1) - USD ($)	3 Months Ended
	Apr. 01, 2017	Apr. 02, 2016
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other than temporary impairment	$ (220,000)	$ 0
Income before income taxes	15,139,000	12,196,000
Tax benefit	(4,928,000)	(3,988,000)
Net income	10,211,000	$ 8,208,000
Total reclassifications for the period	(168,000)
Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	(168,000)
Reclassifications out of Accumulated Other Comprehensive Loss [Member] | Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Realized gain/(loss) on sale of securities	(47,000)
Other than temporary impairment	(220,000)
Income before income taxes	(267,000)
Tax benefit	99,000
Net income	$ (168,000)