Industry Segment and Geographic Area Data (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	Mar. 31, 2014
Quarter ended:
Total revenues	$ 906,491	$ 839,223	$ 1,725,446	$ 1,588,180
Depreciation and amortization, net of (gains) losses on disposals	71,356	69,265	136,591	130,382
Interest expense	24,877	23,118	49,025	46,446
Pretax earnings (loss)	246,878	216,848	441,929	395,896
Income tax expense	90,631	78,857	161,208	144,937
Identifiable assets	6,869,791	5,776,345	6,869,791	5,776,345	5,998,978
United States [Member]
Quarter ended:
Total revenues	852,935	789,453	1,625,978	1,495,542
Depreciation and amortization, net of (gains) losses on disposals	69,845	67,355	133,885	126,525
Interest expense	24,748	22,977	48,767	46,163
Pretax earnings (loss)	237,800	207,480	424,707	379,236
Income tax expense	88,225	76,374	156,644	140,522
Identifiable assets	6,681,237	5,626,460	6,681,237	5,626,460
Canada [Member]
Quarter ended:
Total revenues	53,556	49,770	99,468	92,638
Depreciation and amortization, net of (gains) losses on disposals	1,511	1,910	2,706	3,857
Interest expense	129	141	258	283
Pretax earnings (loss)	9,078	9,368	17,222	16,660
Income tax expense	2,406	2,483	4,564	4,415
Identifiable assets	$ 188,554	$ 149,885	$ 188,554	$ 149,885