Stockholders' Equity (Schedule of Stockholders' Equity) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014		Dec. 31, 2013	Mar. 31, 2014
Class of Stock [Line Items]
Common stock, shares issued	87,504		87,504			87,353
Common stock issuance			151	[1]
Treasury stock, shares	(12,477)		(12,477)			(13,264)
Reissuance of treasury stock for stock option exercises			746
Reissuance of treasury stock for acquisition			41
Dividends paid per common share			$ 1.65
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at March 31, 2014			$ 1,840,649
Net earnings	93,199	82,759	280,363		262,427
Other comprehensive income (loss), net of tax	(5,611)	(1,227)	(8,264)		(1,601)
Common stock issuances and reissuances of treasury stock - employee benefit plans			54,870	[2]
Reissuance of treasury stock for acquisition (Note 3)			4,458
Excess tax benefit from stock option exercises			10,487
Dividends paid on common stock			(123,080)
Stock-based compensation			25,618	[3]
Balance at December 31, 2014	2,085,101		2,085,101
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 December 31, 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			11,936	[2]
Reissuance of treasury stock for acquisition (Note 3)			1,368
Excess tax benefit from stock option exercises			10,487
Stock-based compensation			25,618	[3]
Balance at December 31, 2014	839,198		839,198
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at March 31, 2014			2,047,843
Net earnings			280,363
Reissuance of treasury stock for stock option exercises at lower than repurchase price			(13,187)	[2]
Dividends paid on common stock			(123,080)
Balance at December 31, 2014	2,191,939		2,191,939
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			(8,264)
Balance at December 31, 2014	(7,735)		(7,735)
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			56,120	[2]
Reissuance of treasury stock for acquisition (Note 3)			3,090
Balance at December 31, 2014	$ (939,176)		$ (939,176)

[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.