Comprehensive Income (Components Of Comprehensive Income) (Details) (USD $) In Thousands	3 Months Ended	9 Months Ended
Sep. 24, 2011	Sep. 25, 2010	Sep. 24, 2011	Sep. 25, 2010
Comprehensive Income
Net income attributable to Landstar System, Inc. and subsidiary	$ 30,158	$ 21,802	$ 80,375	$ 63,415
Unrealized holding gains (losses) on available-for-sale investments	(224)	752	230	948
Income tax benefit (expense) on unrealized holding gains (losses) on available-for-sale investments	79	(266)	(82)	(336)
Net unrealized holding gains (losses) on available-for-sale investments	(145)	486	148	612
Foreign currency translation gains (losses)	(44)	14	169	71
Comprehensive income attributable to Landstar System, Inc. and subsidiary	$ 29,969	$ 22,302	$ 80,692	$ 64,098

The change in equity [net assets] of a business enterprise during a period from transactions and other events and circumstances from non-owner sources which are attributable to the reporting entity. It includes all changes in equity during a period except those resulting from investments by owners and distributions to owners, but excludes any and all transactions which are directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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- Definition

Adjustment that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency of the reporting entity, net of tax.

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Gross appreciation or the gross loss in value of the total of unsold available-for-sale securities during the period being reported (except when designated as a fair value hedge).

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Appreciation or loss in value (before reclassification adjustment) of the total of unsold securities during the period being reported on, net of tax. Reclassification adjustments include: (1) the unrealized holding gain (loss), net of tax, at the date of the transfer for a debt security from the held-to-maturity category transferred into the available-for-sale category. Also includes the unrealized gain (loss) at the date of transfer for a debt security from the available-for-sale category transferred into the held-to-maturity category; (2) the unrealized gains (losses) realized upon the sale of securities, after tax; and (3) the unrealized gains (losses) realized upon the write-down of securities, after tax.

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