Industry Segment and Geographic Area Data (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Mar. 31, 2015
Quarter ended:
Total revenues	$ 962,903	$ 906,491	$ 1,847,708	$ 1,725,446
Depreciation and amortization, net of (gains) losses on disposals	68,721	71,356	124,481	136,591
Interest expense	23,973	24,877	46,073	49,025
Pretax earnings	287,095	246,878	556,103	441,929
Income tax expense	103,716	90,631	201,439	161,208
Identifiable assets	7,600,545	6,869,791	7,600,545	6,869,791	$ 6,872,175
United States [Member]
Quarter ended:
Total revenues	915,906	852,935	1,757,369	1,625,978
Depreciation and amortization, net of (gains) losses on disposals	68,983	69,845	125,722	133,885
Interest expense	23,973	24,748	45,962	48,767
Pretax earnings	276,263	237,800	535,390	424,707
Income tax expense	100,926	88,225	196,021	156,644
Identifiable assets	7,376,921	6,681,237	7,376,921	6,681,237
Canada [Member]
Quarter ended:
Total revenues	46,997	53,556	90,339	99,468
Depreciation and amortization, net of (gains) losses on disposals	$ (262)	1,511	(1,241)	2,706
Interest expense		129	111	258
Pretax earnings	$ 10,832	9,078	20,713	17,222
Income tax expense	2,790	2,406	5,418	4,564
Identifiable assets	$ 223,624	$ 188,554	$ 223,624	$ 188,554