Industry Segment and Geographic Area Data (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2017
Quarter ended:
Total revenues	$ 842,882	$ 790,455	$ 2,843,493	$ 2,712,331
Depreciation and amortization, net of (gains) losses on disposals	143,013	123,741	222,534	340,539
Interest expense	31,558	28,782	93,926	83,197
Pretax earnings	271,579	102,700	667,623	614,822
Income tax expense	(257,315)	37,472	(112,117)	225,946
Identifiable assets	10,496,959	9,287,317	10,496,959	9,287,317	$ 9,405,840
United States [Member]
Quarter ended:
Total revenues	805,692	757,477	2,707,614	2,588,121
Depreciation and amortization, net of (gains) losses on disposals	141,193	122,242	216,885	336,618
Interest expense	30,824	28,779	91,735	83,192
Pretax earnings	269,830	99,660	654,388	595,217
Income tax expense	264,361	(36,678)	115,855	(220,695)
Identifiable assets	10,186,992	8,981,335	10,186,992	8,981,335
Canada [Member]
Quarter ended:
Total revenues	37,190	32,978	135,879	124,210
Depreciation and amortization, net of (gains) losses on disposals	1,820	1,499	5,649	3,921
Interest expense	734	3	2,191	5
Pretax earnings	1,749	3,040	13,235	19,605
Income tax expense	(7,046)	794	(3,738)	5,251
Identifiable assets	$ 309,967	$ 305,982	$ 309,967	$ 305,982