Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Mar. 31, 2015		Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share [Abstract]
Anti-dilutive securities excluded from the Company's diluted earnings per share																	1,700,000	1,500,000	1,300,000
Net earnings	$ 87,723	[1]	$ 93,199	[1]	$ 98,312	[1]	$ 88,852	[1]	$ 88,357	[1]	$ 82,759	[1]	$ 94,982	[1]	$ 84,686	[1]	$ 368,086	$ 350,784	$ 340,874
Basic shares outstanding																	74,702,000	73,623,000	76,651,000
Basic earnings per share	$ 1.17	[2]	$ 1.25	[2]	$ 1.32	[2]	$ 1.20	[2]	$ 1.19	[2]	$ 1.12	[2]	$ 1.29	[2]	$ 1.16	[2]	$ 4.93	$ 4.76	$ 4.45
Incremental shares from assumed exercises of stock options and options under the ESPP																	1,149,000	1,287,000	1,656,000
Diluted shares outstanding																	75,851,000	74,910,000	78,307,000
Diluted earnings per share	$ 1.15	[2]	$ 1.23	[2]	$ 1.30	[2]	$ 1.18	[2]	$ 1.17	[2]	$ 1.10	[2]	$ 1.27	[2]	$ 1.14	[2]	$ 4.85	$ 4.68	$ 4.35

[1] Net earnings include the impact of the following non-operating items (after tax)

[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.