Fair Value Measurements (Details) (Recurring [Member], USD $)	Sep. 27, 2014	Dec. 28, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	$ 55,317,000	$ 52,159,000
Marketable debt securities - noncurrent	43,376,000	34,632,000
Marketable debt securities	98,693,000	86,791,000
Deferred compensation plan liability	900,000	1,100,000
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	17,516,000	15,011,000
Marketable debt securities - noncurrent	14,996,000	8,978,000
Marketable debt securities	32,512,000	23,989,000
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	37,801,000	37,148,000
Marketable debt securities - noncurrent	28,380,000	25,654,000
Marketable debt securities	66,181,000	62,802,000
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	0	0
Marketable debt securities - noncurrent	0	0
Marketable debt securities	0	0
Available-for-sale Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities assets funding the deferred compensation plan	900,000	1,100,000
US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	17,516,000	15,011,000
Marketable debt securities - noncurrent	14,996,000	8,978,000
US Treasury Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	17,516,000	15,011,000
Marketable debt securities - noncurrent	14,996,000	8,978,000
US Treasury Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	0	0
Marketable debt securities - noncurrent	0	0
US Treasury Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	0	0
Marketable debt securities - noncurrent	0	0
Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	17,736,000	20,300,000
Marketable debt securities - noncurrent	15,242,000	15,484,000
Corporate bonds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	0	0
Marketable debt securities - noncurrent	0	0
Corporate bonds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	17,736,000	20,300,000
Marketable debt securities - noncurrent	15,242,000	15,484,000
Corporate bonds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	0	0
Marketable debt securities - noncurrent	0	0
U.S. Agency bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	9,544,000	12,025,000
Marketable debt securities - noncurrent	10,019,000	7,498,000
U.S. Agency bonds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	0	0
Marketable debt securities - noncurrent	0	0
U.S. Agency bonds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	9,544,000	12,025,000
Marketable debt securities - noncurrent	10,019,000	7,498,000
U.S. Agency bonds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	0	0
Marketable debt securities - noncurrent	0	0
Municipal bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	5,526,000	4,823,000
Marketable debt securities - noncurrent	3,119,000	2,672,000
Municipal bonds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	0	0
Marketable debt securities - noncurrent	0	0
Municipal bonds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	5,526,000	4,823,000
Marketable debt securities - noncurrent	3,119,000	2,672,000
Municipal bonds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	0	0
Marketable debt securities - noncurrent	0	0
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	4,995,000
Commercial Paper [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	0
Commercial Paper [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	4,995,000
Commercial Paper [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	$ 0