Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Earnings Per Share [Abstract]
Anti-dilutive securities excluded from the Company's diluted earnings per share																	1,300,000	1,800,000	1,300,000
Net earnings	$ 86,140		$ 82,915		$ 81,020		$ 90,798	[1]	$ 87,967	[1]	$ 72,559		$ 77,854		$ 74,994		$ 340,874	$ 313,374	$ 250,264
Basic shares outstanding																	76,651,000	76,586,000	83,487,000
Basic earnings per share	$ 1.15	[2]	$ 1.07	[2]	$ 1.05	[2]	$ 1.18	[2]	$ 1.15	[2]	$ 0.96	[2]	$ 1.03	[2]	$ 0.96	[2]	$ 4.45	$ 4.09	$ 3.00
Incremental shares from assumed exercises of stock options and options under the ESPP																	1,656,000	1,738,000	1,765,000
Diluted shares outstanding																	78,307,000	78,324,000	85,252,000
Diluted earnings per share	$ 1.13	[2]	$ 1.05	[2]	$ 1.03	[2]	$ 1.15	[2]	$ 1.12	[2]	$ 0.93	[2]	$ 1.01	[2]	$ 0.94	[2]	$ 4.35	$ 4.00	$ 2.94

[1] Net earnings for the first quarter of fiscal 2013 include a $6.8 million ($5.5 million after tax) gain on the sale of businesses related to the divestiture of the assets and operations of five branch locations in western Canada. Net earnings for the fourth quarter of fiscal 2012 include a $4.9 million income tax benefit related to the LLC reorganization as well as a true-up of the Company’s foreign tax liabilities.

[2] Earnings per share calculations for each of the quarters are based on the weighted average number of shares outstanding in each quarter. Therefore, the sum of the quarterly earnings per share does not necessarily equal the full year earnings per share disclosed on the Consolidated Statements of Earnings.