Summary by Business Segment (Financial Information by Segment) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Segment Reporting Information [Line Items]
Net Sales	$ 1,357,755		$ 1,281,970		$ 2,671,342		$ 2,561,861
Cost of products sold (excluding depreciation)	600,534		563,012		1,183,940		1,138,555
Selling, distribution and administrative expenses	500,375		474,455		995,088		947,930
Depreciation	73,160		68,487		145,795		135,517
Amortization	7,905		7,247		15,657		14,476
Total costs and expenses	1,181,974		1,113,201		2,340,480		2,236,478
Operating Income	175,781		168,769		330,862		325,383
Gas and Rent [Member]
Segment Reporting Information [Line Items]
Net Sales	858,515		822,786		1,684,106		1,632,678
Hardgoods [Member]
Segment Reporting Information [Line Items]
Net Sales	499,240		459,184		987,236		929,183
Operating Segments [Member] | Distribution Business Segment [Member]
Segment Reporting Information [Line Items]
Net Sales	1,217,010		1,139,576		2,400,622		2,280,660
Cost of products sold (excluding depreciation)	531,867		491,660		1,052,800		996,787
Selling, distribution and administrative expenses	452,467		427,351		902,106		854,582
Depreciation	66,949		62,865		133,411		124,529
Amortization	6,881		6,193		13,605		12,255
Total costs and expenses	1,058,164		988,069		2,101,922		1,988,153
Operating Income	158,846		151,507		298,700		292,507
Operating Segments [Member] | Distribution Business Segment [Member] | Gas and Rent [Member]
Segment Reporting Information [Line Items]
Net Sales	718,743		681,389		1,415,308		1,353,875
Operating Segments [Member] | Distribution Business Segment [Member] | Hardgoods [Member]
Segment Reporting Information [Line Items]
Net Sales	498,267		458,187		985,314		926,785
Operating Segments [Member] | All Other Operations Business Segment [Member]
Segment Reporting Information [Line Items]
Net Sales	148,795		150,310		285,838		297,580
Cost of products sold (excluding depreciation)	76,717		79,268		146,258		158,147
Selling, distribution and administrative expenses	47,908		45,412		92,982		88,952
Depreciation	6,211		5,622		12,384		10,988
Amortization	1,024		1,054		2,052		2,221
Total costs and expenses	131,860		131,356		253,676		260,308
Operating Income	16,935		18,954		32,162		37,272
Operating Segments [Member] | All Other Operations Business Segment [Member] | Gas and Rent [Member]
Segment Reporting Information [Line Items]
Net Sales	147,821		149,313		283,913		295,180
Operating Segments [Member] | All Other Operations Business Segment [Member] | Hardgoods [Member]
Segment Reporting Information [Line Items]
Net Sales	974		997		1,925		2,400
Eliminations and Other [Member]
Segment Reporting Information [Line Items]
Net Sales	(8,050)	[1]	(7,916)	[1]	(15,118)	[1]	(16,379)	[1]
Cost of products sold (excluding depreciation)	(8,050)	[1]	(7,916)	[1]	(15,118)	[1]	(16,379)	[1]
Selling, distribution and administrative expenses	0		1,692		0		4,396
Depreciation	0		0		0		0
Amortization	0		0		0		0
Total costs and expenses	(8,050)		(6,224)		(15,118)		(11,983)
Operating Income	0		(1,692)		0		(4,396)
Eliminations and Other [Member] | Gas and Rent [Member]
Segment Reporting Information [Line Items]
Net Sales	(8,049)		(7,916)		(15,115)		(16,377)
Eliminations and Other [Member] | Hardgoods [Member]
Segment Reporting Information [Line Items]
Net Sales	$ (1)		$ 0		$ (3)		$ (2)

[1] Amounts in the “Eliminations and Other” column represent the elimination of intercompany sales and associated gross profit on sales from the Company’s All Other Operations business segment to its Distribution business segment.