Industry Segment and Geographic Area Data (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Mar. 31, 2021
Quarter ended:
Total revenues	$ 1,664,254	$ 1,324,908	$ 3,137,110	$ 2,312,145
Depreciation and amortization, net of (gains) losses on disposals	143,021	146,415	269,131	318,718
Interest expense	39,545	40,525	78,723	80,046
Pretax earnings (loss)	538,876	351,019	993,626	465,337
Income tax expense	128,978	84,654	238,553	111,246
Identifiable assets	16,337,228	14,123,478	16,337,228	14,123,478	$ 14,651,606
United States [Member]
Quarter ended:
Total revenues	1,576,830	1,261,235	2,973,191	2,204,038
Depreciation and amortization, net of (gains) losses on disposals	141,956	144,222	269,606	312,748
Interest expense	38,588	39,983	76,716	78,637
Pretax earnings (loss)	521,658	340,200	959,607	452,149
Income tax expense	124,620	81,624	229,922	107,407
Identifiable assets	15,849,380	13,693,016	15,849,380	13,693,016
Canada [Member]
Quarter ended:
Total revenues	87,424	63,673	163,919	108,107
Depreciation and amortization, net of (gains) losses on disposals	1,065	2,193	(475)	5,970
Interest expense	957	542	2,007	1,409
Pretax earnings (loss)	17,218	10,819	34,019	13,188
Income tax expense	4,358	3,030	8,631	3,839
Identifiable assets	$ 487,848	$ 430,462	$ 487,848	$ 430,462