Quarterly Financial Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 29, 2012		Sep. 29, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 24, 2011		Jun. 25, 2011		Mar. 26, 2011		Dec. 29, 2012	Dec. 31, 2011	Dec. 25, 2010
Quarterly Financial Information [Line Items]
Revenue	$ 691,256		$ 717,168		$ 735,973		$ 649,023		$ 717,522		$ 684,013		$ 675,561		$ 571,986		$ 2,793,420	$ 2,649,082	$ 2,400,170
Operating income	49,535		54,379		58,789		43,150		50,950		49,533		48,670		34,092		205,853	183,245	139,971
Income before income taxes	48,743		53,561		58,019		42,426		50,178		48,798		47,893		33,264		202,749	180,133	136,348
Income taxes	14,765		20,460		22,164		15,579		17,546		18,640		18,295		12,707		72,968	67,188	49,766
Net income	33,978		33,101		35,855		26,847		32,632		30,158		29,598		20,557		129,781	112,945	86,582
Less: Net loss attributable to noncontrolling interest															(62)			(62)	(932)
Net income attributable to Landstar System, Inc. and subsidiary									$ 32,632		$ 30,158		$ 29,598		$ 20,619		$ 129,781	$ 113,007	$ 87,514
Earnings per common share attributable to Landstar System, Inc. and subsidiary	$ 0.73	[1]	$ 0.71	[1]	$ 0.76	[1]	$ 0.57	[1]	$ 0.70	[1]	$ 0.64	[1]	$ 0.62	[1]	$ 0.43	[1]	$ 2.78	$ 2.38	$ 1.77
Diluted earnings per share attributable to Landstar System, Inc. and subsidiary	$ 0.73	[1]	$ 0.71	[1]	$ 0.76	[1]	$ 0.57	[1]	$ 0.70	[1]	$ 0.64	[1]	$ 0.62	[1]	$ 0.43	[1]	$ 2.77	$ 2.38	$ 1.77
Dividends paid per common share	$ 0.560		$ 0.060		$ 0.055		$ 0.055		$ 0.055		$ 0.055		$ 0.050		$ 0.050		$ 0.73	$ 0.21	$ 0.19

[1] Due to the changes in the number of average common shares and common stock equivalents outstanding during the year, the sum of earnings per share amounts for each quarter do not necessarily sum in the aggregate to the earnings per share amounts for the full year.