Quarterly Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2011		Sep. 24, 2011		Jun. 25, 2011		Mar. 26, 2011		Dec. 25, 2010		Sep. 25, 2010		Jun. 26, 2010		Mar. 27, 2010		Dec. 31, 2011	Dec. 25, 2010	Dec. 26, 2009
Quarterly Financial Data [Abstract]
Revenue	$ 717,522		$ 684,013		$ 675,561		$ 571,986		$ 587,535		$ 622,826		$ 641,721		$ 548,088		$ 2,649,082	$ 2,400,170	$ 2,008,796
Operating income	50,950		49,533		48,670		34,092		35,808		35,886		39,982		28,295		183,245	139,971	113,742
Income before income taxes	50,178		48,798		47,893		33,264		34,884		34,851		39,172		27,441		180,133	136,348	109,712
Income taxes	17,546		18,640		18,295		12,707		11,005		13,315		14,962		10,484		67,188	49,766	39,762
Net income	32,632		30,158		29,598		20,557		23,879		21,536		24,210		16,957		112,945	86,582	69,950
Less: Net loss attributable to noncontrolling interest							(62)		(220)		(266)		(227)		(219)		(62)	(932)	(445)
Net income attributable to Landstar System, Inc. and subsidiary	$ 32,632		$ 30,158		$ 29,598		$ 20,619		$ 24,099		$ 21,802		$ 24,437		$ 17,176		$ 113,007	$ 87,514	$ 70,395
Earnings per common share attributable to Landstar System, Inc. and subsidiary	$ 0.70	[1]	$ 0.64	[1]	$ 0.62	[1]	$ 0.43	[1]	$ 0.50	[1]	$ 0.44	[1]	$ 0.49	[1]	$ 0.34	[1]	$ 2.38	$ 1.77	$ 1.38
Diluted earnings per share attributable to Landstar System, Inc. and subsidiary	$ 0.70	[1]	$ 0.64	[1]	$ 0.62	[1]	$ 0.43	[1]	$ 0.50	[1]	$ 0.44	[1]	$ 0.49	[1]	$ 0.34	[1]	$ 2.38	$ 1.77	$ 1.37
Dividends paid per common share	$ 0.055		$ 0.055		$ 0.050		$ 0.050		$ 0.050		$ 0.050		$ 0.045		$ 0.045		$ 0.21	$ 0.19	$ 0.17

[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.