Industry Segment and Geographic Area Data (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2016
Quarter ended:
Total revenues	$ 790,676	$ 744,751	$ 2,712,996	$ 2,592,459
Depreciation and amortization, net of (gains) losses on disposals	121,323	90,851	340,539	215,332
Interest expense	29,003	25,407	83,862	71,480
Pretax earnings	102,700	132,495	614,822	688,598
Income tax expense	37,472	50,726	225,946	252,165
Identifiable assets	9,287,317	7,762,534	9,287,317	7,762,534	$ 8,127,363
United States [Member]
Quarter ended:
Total revenues	757,698	713,416	2,588,786	2,470,785
Depreciation and amortization, net of (gains) losses on disposals	119,824	90,273	336,618	215,995
Interest expense	29,000	25,357	83,857	71,319
Pretax earnings	99,660	128,799	595,217	664,189
Income tax expense	36,678	49,776	220,695	245,797
Identifiable assets	8,981,335	7,534,725	8,981,335	7,534,725
Canada [Member]
Quarter ended:
Total revenues	32,978	31,335	124,210	121,674
Depreciation and amortization, net of (gains) losses on disposals	1,499	578	3,921	(663)
Interest expense	3	50	5	161
Pretax earnings	3,040	3,696	19,605	24,409
Income tax expense	794	950	5,251	6,368
Identifiable assets	$ 305,982	$ 227,809	$ 305,982	$ 227,809