Financial Information by Geographic Area (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Fiscal year ended:
Total revenues	$ 3,601,114	$ 3,421,767	$ 3,275,468
Depreciation and amortization, net of (gains) losses on disposals	372,347	471,653	313,962
Interest expense	126,706	113,406	97,715
Pretax earnings	637,613	628,358	768,911
Income tax expense	(152,970)	229,934	279,910
Identifiable assets	10,746,985	9,405,840	8,109,288
United States [Member]
Fiscal year ended:
Total revenues	3,435,821	3,271,563	3,129,909
Depreciation and amortization, net of (gains) losses on disposals	363,826	466,378	313,099
Interest expense	123,777	112,834	97,551
Pretax earnings	628,901	609,589	745,194
Income tax expense	(155,685)	225,278	273,473
Identifiable assets	10,424,862	9,030,528	7,859,928
Canada [Member]
Fiscal year ended:
Total revenues	165,293	150,204	145,559
Depreciation and amortization, net of (gains) losses on disposals	8,521	5,275	863
Interest expense	2,929	572	164
Pretax earnings	8,712	18,769	23,717
Income tax expense	2,715	4,656	6,437
Identifiable assets	$ 322,123	$ 375,312	$ 249,360