Stockholders' Equity (Schedule of Stockholders' Equity) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2013	Mar. 31, 2014
Class of Stock [Line Items]
Common stock, shares issued	87,456		87,456			87,353
Common stock issuance during period, shares, Employee Stock Purchase Plan			103	[1]
Treasury stock, shares	(12,842)		(12,842)			(13,264)
Reissuance of treasury stock for stock option exercises			381
Reissuance of treasury stock for acquisition			41
Dividends paid per common share			$ 1.10
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at March 31, 2014			$ 1,840,649
Net earnings	98,312	94,982	187,164		179,668
Other comprehensive income (loss), net of tax	(5,310)	2,109	(2,653)		(374)
Common stock issuances and reissuances of treasury stock - employee benefit plans			28,824	[2]
Reissuance of treasury stock for acquisition (Note 3)			4,458
Excess tax benefit from stock option exercises			5,091
Dividends paid on common stock			(81,942)
Stock-based compensation			20,833	[3]
Balance at September 30, 2014	2,002,424		2,002,424
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at March 31, 2014			874
Issuance of common stock for purchases through the Employee Stock Purchase Plan			1	[2]
Balance at September 30, 2014	875		875
Capital In Excess of Par Value [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at March 31, 2014			789,789
Common stock issuances and reissuances of treasury stock - employee benefit plans			7,626	[2]
Reissuance of treasury stock for acquisition (Note 3)			1,368
Excess tax benefit from stock option exercises			5,091
Stock-based compensation			20,833	[3]
Balance at September 30, 2014	824,707		824,707
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at March 31, 2014			2,047,843
Net earnings			187,164
Reissuance of treasury stock for stock option exercises at lower than repurchase price			(7,436)	[2]
Dividends paid on common stock			(81,942)
Balance at September 30, 2014	2,145,629		2,145,629
Accumulated Other Comprehensive Income [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at March 31, 2014			529
Other comprehensive income (loss), net of tax			(2,653)
Balance at September 30, 2014	(2,124)		(2,124)
Treasury Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at March 31, 2014			(998,386)
Reissuance of treasury stock for stock option exercises			28,633	[2]
Reissuance of treasury stock for acquisition (Note 3)			3,090
Balance at September 30, 2014	$ (966,663)		$ (966,663)

[1] Issuance of common stock for purchases through the Employee Stock Purchase Plan.

[2] Issuance of common stock for purchases through the Employee Stock Purchase Plan and reissuance of treasury stock for stock option exercises.

[3] The Company recognized compensation expense with a corresponding amount recorded to capital in excess of par value.