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, 2013	Dec. 31, 2012	Dec. 31, 2013		Dec. 31, 2012	Mar. 31, 2013
Class of Stock [Line Items]
Common stock, shares, issued	87,301		87,301			87,135
Common stock issuance during period, shares, Employee Stock Purchase Plans			166	[1]
Treasury stock, shares	(13,472)		(13,472)			(14,077)
Reissuance of treasury stock for stock option exercises, shares			605
Common Stock, Dividends, Per Share, Cash Paid			$ 1.44
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at March 31, 2013			$ 1,536,983
Net Earnings	82,759	82,915	262,427		254,733
Other comprehensive income (loss), net of tax	(1,227)	(54)	(1,601)		605
Stock Issued During Period, Value, Employee Stock Purchase Plan			42,745	[2]
Excess tax benefit from stock option exercises			9,426
Dividends paid on common stock ($1.44 per share)			(105,936)		(92,655)
Stock-based compensation			24,542	[3]
Balance at December 31, 2013	1,768,586		1,768,586
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at March 31, 2013			871
Stock Issued During Period, Value, Employee Stock Purchase Plan			2	[2]
Balance at December 31, 2013	873		873
Capital In Excess of Par Value [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at March 31, 2013			729,850
Stock Issued During Period, Value, Employee Stock Purchase Plan			12,972	[2]
Excess tax benefit from stock option exercises			9,426
Stock-based compensation			24,542	[3]
Balance at December 31, 2013	776,790		776,790
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at March 31, 2013			1,861,395
Net Earnings			262,427
Treasury Stock Reissued at Lower than Repurchase Price			(15,740)	[2]
Dividends paid on common stock ($1.44 per share)			(105,936)
Balance at December 31, 2013	2,002,146		2,002,146
Accumulated Other Comprehensive Income [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at March 31, 2013			4,438
Other comprehensive income (loss), net of tax			(1,601)
Balance at December 31, 2013	2,837		2,837
Treasury Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at March 31, 2013			(1,059,571)
Stock Issued During Period, Value, Treasury Stock Reissued for Stock Option Exercises			45,511	[2]
Balance at December 31, 2013	$ (1,014,060)		$ (1,014,060)

[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.