Industry Segment and Geographic Area Data (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Mar. 31, 2021
Quarter ended:
Total revenues	$ 1,404,336	$ 1,169,982	$ 4,541,446	$ 3,482,127
Depreciation and amortization, net of (gains) losses on disposals	112,660	160,298	381,791	479,016
Interest expense	44,042	42,128	122,765	122,174
Pretax earnings (loss)	371,446	241,571	1,365,072	706,908
Income tax expense	89,980	58,586	328,533	169,832
Identifiable assets	16,588,078	14,447,305	16,588,078	14,447,305	$ 14,651,606
United States [Member]
Quarter ended:
Total revenues	1,334,131	1,114,816	4,307,322	3,318,854
Depreciation and amortization, net of (gains) losses on disposals	110,383	158,844	379,989	471,592
Interest expense	43,140	41,378	119,856	120,015
Pretax earnings (loss)	360,449	233,163	1,320,056	685,312
Income tax expense	87,135	56,237	317,057	163,644
Identifiable assets	16,077,571	14,020,573	16,077,571	14,020,573
Canada [Member]
Quarter ended:
Total revenues	70,205	55,166	234,124	163,273
Depreciation and amortization, net of (gains) losses on disposals	2,277	1,454	1,802	7,424
Interest expense	902	750	2,909	2,159
Pretax earnings (loss)	10,997	8,408	45,016	21,596
Income tax expense	2,845	2,349	11,476	6,188
Identifiable assets	$ 510,507	$ 426,732	$ 510,507	$ 426,732