Industry Segment and Geographic Area Data (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Mar. 31, 2014
Quarter ended:
Total revenues	$ 706,355	$ 645,331	$ 2,431,801	$ 2,233,511
Depreciation and amortization, net of (gains) losses on disposals	86,532	75,246	223,123	205,628
Interest expense	25,719	23,607	74,744	70,053
Pretax earnings (loss)	107,433	82,366	549,362	478,262
Income tax expense	40,893	30,145	202,101	175,082
Identifiable assets	6,906,532	5,874,109	6,906,532	5,874,109	5,998,978
United States [Member]
Quarter ended:
Total revenues	671,311	611,428	2,297,289	2,106,970
Depreciation and amortization, net of (gains) losses on disposals	85,038	73,684	218,923	200,209
Interest expense	25,580	23,470	74,347	69,633
Pretax earnings (loss)	104,830	78,745	529,537	457,981
Income tax expense	40,203	29,186	196,847	169,708
Identifiable assets	6,715,544	5,731,164	6,715,544	5,731,164
Canada [Member]
Quarter ended:
Total revenues	35,044	33,903	134,512	126,541
Depreciation and amortization, net of (gains) losses on disposals	1,494	1,562	4,200	5,419
Interest expense	139	137	397	420
Pretax earnings (loss)	2,603	3,621	19,825	20,281
Income tax expense	690	959	5,254	5,374
Identifiable assets	$ 190,988	$ 142,945	$ 190,988	$ 142,945