Fair Value Measurements (Details) (Recurring [Member], USD $)	Jan. 03, 2015	Dec. 28, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	$ 69,609,000	$ 52,159,000
Marketable debt securities - noncurrent	44,441,000	34,632,000
Marketable debt securities	114,050,000	86,791,000
Deferred compensation plan liability	1,000,000	1,100,000
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	17,506,000	15,011,000
Marketable debt securities - noncurrent	14,990,000	8,978,000
Marketable debt securities	32,496,000	23,989,000
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	52,103,000	37,148,000
Marketable debt securities - noncurrent	29,451,000	25,654,000
Marketable debt securities	81,554,000	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]
Deferred Compensation Plan Assets	1,000,000	1,100,000
US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	17,506,000	15,011,000
Marketable debt securities - noncurrent	14,990,000	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	17,506,000	15,011,000
Marketable debt securities - noncurrent	14,990,000	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	20,139,000	20,300,000
Marketable debt securities - noncurrent	15,236,000	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	20,139,000	20,300,000
Marketable debt securities - noncurrent	15,236,000	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	12,525,000	12,025,000
Marketable debt securities - noncurrent	10,014,000	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	12,525,000	12,025,000
Marketable debt securities - noncurrent	10,014,000	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	6,953,000	4,823,000
Marketable debt securities - noncurrent	4,201,000	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	6,953,000	4,823,000
Marketable debt securities - noncurrent	4,201,000	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, Not Included with Cash and Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	12,486,000
Commercial Paper, Not Included with Cash and Cash Equivalents [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	0
Commercial Paper, Not Included with Cash and Cash Equivalents [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	12,486,000
Commercial Paper, Not Included with Cash and Cash Equivalents [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities - current	$ 0