Stockholders' Equity (Schedule of Stockholders' Equity) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		4 Months Ended	6 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2015		Sep. 30, 2014	Mar. 31, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, shares issued at March 31, 2015					87,554
Common stock issuance	[1]				108
Common stock, shares issued at September 30, 2015		87,662		87,662	87,662
Treasury stock, shares at March 31, 2015					(12,197)
Reissuance of treasury stock for stock option exercises					270
Purchase of treasury stock		(2,800)		(3,800)	(3,764)	[2]
Treasury stock, shares at September 30, 2015		(15,691)		(15,691)	(15,691)
Stockholders' equity balance at March 31, 2015					$ 2,151,586
Net earnings		$ 98,034	$ 98,312		186,269		$ 187,164
Other comprehensive income (loss), net of tax		(4,965)	$ (5,310)		(3,073)		$ (2,653)
Common stock issuances and reissuances of treasury stock - employee benefit plans	[3]				21,755
Purchase of treasury stock	[2]				(374,706)
Excess tax benefit from stock option exercises					4,233
Dividends paid on common stock ($1.20 per share)					(88,515)
Stock-based compensation	[4]				19,572
Stockholders' equity balance at September 30, 2015		$ 1,917,121		$ 1,917,121	$ 1,917,121
Common stock, par value		$ 0.01		$ 0.01	$ 0.01			$ 0.01
Dividends paid per common share					$ 1.20
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' equity balance at March 31, 2015					$ 876
Issuance of common stock for purchases through the Employee Stock Purchase Plan	[3]				1
Stockholders' equity balance at September 30, 2015		$ 877		$ 877	877
Capital In Excess of Par Value [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' equity balance at March 31, 2015					853,800
Common stock issuances and reissuances of treasury stock - employee benefit plans	[3]				9,613
Excess tax benefit from stock option exercises					4,233
Stock-based compensation	[4]				19,572
Stockholders' equity balance at September 30, 2015		887,218		887,218	887,218
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' equity balance at March 31, 2015					2,231,026
Net earnings					186,269
Reissuance of treasury stock for stock option exercises at lower than repurchase price	[3]				(8,744)
Dividends paid on common stock ($1.20 per share)					(88,515)
Stockholders' equity balance at September 30, 2015		2,320,036		2,320,036	2,320,036
Accumulated Other Comprehensive Income [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' equity balance at March 31, 2015					(14,853)
Other comprehensive income (loss), net of tax					(3,073)
Stockholders' equity balance at September 30, 2015		(17,926)		(17,926)	(17,926)
Treasury Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' equity balance at March 31, 2015					(919,263)
Reissuance of treasury stock for stock option exercises	[3]				20,885
Purchase of treasury stock	[2]				(374,706)
Stockholders' equity balance at September 30, 2015		$ (1,273,084)		$ (1,273,084)	$ (1,273,084)

[1] Issuance of common stock for purchases through the Amended and Restated 2003 Employee Stock Purchase Plan (“Employee Stock Purchase Plan” or “ESPP”).

[2] Refer to “Stock Repurchase Program” section below for details.

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

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