Industry Segment and Geographic Area Data (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Mar. 31, 2013
Quarter and six months ended:
Total revenues	$ 836,491	$ 744,117	$ 1,583,322	$ 1,411,793
Depreciation and amortization, net of (gains) losses on disposals	69,265	62,042	130,382	120,978
Interest expense	23,118	22,113	46,446	45,604
Pretax earnings	216,848	172,209	395,896	299,597
Income tax expense	78,857	62,789	144,937	109,608
Identifiable assets	5,776,345	5,136,964	5,776,345	5,136,964	5,306,601
United States
Quarter and six months ended:
Total revenues	786,721	695,622	1,490,684	1,321,805
Depreciation and amortization, net of (gains) losses on disposals	67,355	59,972	126,525	116,935
Interest expense	22,977	21,961	46,163	45,300
Pretax earnings	207,480	162,693	379,236	282,077
Income tax expense	76,374	60,267	140,522	104,965
Identifiable assets	5,626,460	4,984,218	5,626,460	4,984,218
Canada
Quarter and six months ended:
Total revenues	49,770	48,495	92,638	89,988
Depreciation and amortization, net of (gains) losses on disposals	1,910	2,070	3,857	4,043
Interest expense	141	152	283	304
Pretax earnings	9,368	9,516	16,660	17,520
Income tax expense	2,483	2,522	4,415	4,643
Identifiable assets	$ 149,885	$ 152,746	$ 149,885	$ 152,746