Industry Segment and Geographic Area Data (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2013
Quarter and nine months ended:
Total revenues	$ 641,346	$ 582,487	$ 2,224,668	$ 1,994,280
Depreciation and amortization, net of (gains) losses on disposals	75,246	65,790	205,628	186,768
Interest expense	23,607	22,076	70,053	67,680
Pretax earnings	82,366	59,870	478,262	359,467
Income tax expense	30,145	23,024	175,082	132,632
Identifiable assets	5,874,109	5,219,305	5,874,109	5,219,305	5,306,601
United States
Quarter and nine months ended:
Total revenues	607,443	549,611	2,098,127	1,871,416
Depreciation and amortization, net of (gains) losses on disposals	73,684	63,801	200,209	180,736
Interest expense	23,470	21,926	69,633	67,226
Pretax earnings	78,745	58,669	457,981	340,746
Income tax expense	29,186	22,706	169,708	127,671
Identifiable assets	5,731,164	5,077,479	5,731,164	5,077,479
Canada
Quarter and nine months ended:
Total revenues	33,903	32,876	126,541	122,864
Depreciation and amortization, net of (gains) losses on disposals	1,562	1,989	5,419	6,032
Interest expense	137	150	420	454
Pretax earnings	3,621	1,201	20,281	18,721
Income tax expense	959	318	5,374	4,961
Identifiable assets	$ 142,945	$ 141,826	$ 142,945	$ 141,826