Industry Segment and Geographic Area Data (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2018
Quarter ended:
Total revenues	$ 919,091	$ 842,882	$ 3,043,175	$ 2,843,493
Depreciation and amortization, net of (gains) losses on disposals	150,127	(49,391)	421,119	222,534
Interest expense	34,827	31,558	105,111	93,926
Pretax earnings	103,022	271,579	487,879	667,623
Income tax (expense) benefit	(24,387)	257,315	(117,853)	112,117
Identifiable assets	11,645,760	10,496,959	11,645,760	10,496,959	$ 10,747,422
United States [Member]
Quarter ended:
Total revenues	880,767	805,692	2,901,908	2,707,614
Depreciation and amortization, net of (gains) losses on disposals	147,868	(51,211)	416,784	216,885
Interest expense	34,051	30,824	102,924	91,735
Pretax earnings	100,832	269,830	472,302	654,388
Income tax (expense) benefit	(23,828)	264,361	(113,712)	115,855
Identifiable assets	11,285,627	10,186,992	11,285,627	10,186,992
Canada [Member]
Quarter ended:
Total revenues	38,324	37,190	141,267	135,879
Depreciation and amortization, net of (gains) losses on disposals	2,259	1,820	4,335	5,649
Interest expense	776	734	2,187	2,191
Pretax earnings	2,190	1,749	15,577	13,235
Income tax (expense) benefit	(559)	(7,046)	(4,141)	(3,738)
Identifiable assets	$ 360,133	$ 309,967	$ 360,133	$ 309,967