Fair Value Measurements (Details) (Recurring [Member], USD $) | Jun. 28, 2014 | Dec. 28, 2013 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Marketable debt securities - current | $45,831,000 | $52,159,000 |
Marketable debt securities - noncurrent | 37,822,000 | 34,632,000 |
Marketable debt securities | 83,653,000 | 86,791,000 |
Deferred compensation plan liability | 1,100,000 | 1,100,000 |
Level 1 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Marketable debt securities - current | 7,505,000 | 15,011,000 |
Marketable debt securities - noncurrent | 16,494,000 | 8,978,000 |
Marketable debt securities | 23,999,000 | 23,989,000 |
Marketable securities assets funding the deferred compensation plan | 1,100,000 | 1,100,000 |
Level 2 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Marketable debt securities - current | 38,326,000 | 37,148,000 |
Marketable debt securities - noncurrent | 21,328,000 | 25,654,000 |
Marketable debt securities | 59,654,000 | 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 |
US Treasury Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Marketable debt securities - current | 7,505,000 | 15,011,000 |
Marketable debt securities - noncurrent | 16,494,000 | 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 | 7,505,000 | 15,011,000 |
Marketable debt securities - noncurrent | 16,494,000 | 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 | 22,851,000 | 20,300,000 |
Marketable debt securities - noncurrent | 7,640,000 | 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 | 22,851,000 | 20,300,000 |
Marketable debt securities - noncurrent | 7,640,000 | 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 | 9,508,000 | 12,025,000 |
Marketable debt securities - noncurrent | 10,005,000 | 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 | 9,508,000 | 12,025,000 |
Marketable debt securities - noncurrent | 10,005,000 | 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 | 5,967,000 | 4,823,000 |
Marketable debt securities - noncurrent | 3,683,000 | 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 | 5,967,000 | 4,823,000 |
Marketable debt securities - noncurrent | 3,683,000 | 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 |