Industry Segment and Geographic Area Data (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2020
Quarter ended:
Total revenues	$ 1,169,982	$ 927,880	$ 3,482,127	$ 3,157,343
Depreciation and amortization, net of (gains) losses on disposals	160,298	178,648	479,016	481,541
Interest expense	42,128	39,973	122,174	117,983
Pretax earnings (loss)	241,571	40,329	706,908	420,397
Income tax expense	58,586	9,397	169,832	100,717
Identifiable assets	14,447,305	12,994,322	14,447,305	12,994,322	$ 13,438,024
United States [Member]
Quarter ended:
Total revenues	1,114,816	886,731	3,318,854	3,008,067
Depreciation and amortization, net of (gains) losses on disposals	158,844	174,669	471,592	471,535
Interest expense	41,378	39,042	120,015	115,523
Pretax earnings (loss)	233,163	40,606	685,312	411,565
Income tax expense	56,237	9,303	163,644	97,951
Identifiable assets	14,020,573	12,575,914	14,020,573	12,575,914
Canada [Member]
Quarter ended:
Total revenues	55,166	41,149	163,273	149,276
Depreciation and amortization, net of (gains) losses on disposals	1,454	3,979	7,424	10,006
Interest expense	750	931	2,159	2,460
Pretax earnings (loss)	8,408	(277)	21,596	8,832
Income tax expense	2,349	94	6,188	2,766
Identifiable assets	$ 426,732	$ 418,408	$ 426,732	$ 418,408