Financial Information by Geographic Area (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Fiscal year ended:
Total revenues	$ 3,421,767	$ 3,275,468	$ 3,074,531
Depreciation and amortization, net of (gains) losses on disposals	471,653	313,962	297,826
Interest expense	113,406	97,715	97,525
Pretax earnings	628,358	768,911	561,418
Income tax expense	229,934	279,910	204,677
Identifiable assets	9,405,840	8,109,288	6,855,600
United States [Member]
Fiscal year ended:
Total revenues	3,271,563	3,129,909	2,916,027
Depreciation and amortization, net of (gains) losses on disposals	466,378	313,099	292,345
Interest expense	112,834	97,551	96,979
Pretax earnings	609,589	745,194	541,371
Income tax expense	225,278	273,473	199,444
Identifiable assets	9,030,528	7,859,928	6,668,997
Canada [Member]
Fiscal year ended:
Total revenues	150,204	145,559	158,504
Depreciation and amortization, net of (gains) losses on disposals	5,275	863	5,481
Interest expense	572	164	546
Pretax earnings	18,769	23,717	20,047
Income tax expense	4,656	6,437	5,233
Identifiable assets	$ 375,312	$ 249,360	$ 186,603