Fair Value of Financial Instruments Unobservable Inputs (Details) (USD $)	3 Months Ended
Mar. 30, 2013	Mar. 31, 2012
Short-term marketable securities \| Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Unrealized loss	$ 100,000	$ 100,000
Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning fair value of Long-term marketable securities	4,717,000	6,946,000
Fair value of securities sold or redeemed	0	0
Ending fair value of Long-term marketable securities	$ 4,717,000	$ 6,946,000

This item represents the pretax change in net unrealized holding gain (loss) on available-for-sale securities that has been included in accumulated other comprehensive income, a separate component of shareholders' equity, during the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 21

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27357-111563

Name:	us-gaap_AvailableForSaleSecuritiesChangeInNetUnrealizedHoldingGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration