Industry Segment and Geographic Area Data (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2021
Quarter ended:
Total revenues	$ 1,472,856	$ 987,237
Depreciation and amortization, net of (gains) losses on disposals	126,110	172,303
Interest expense	39,178	39,521
Pretax earnings (loss)	454,750	114,318
Income tax expense	109,575	26,592
Identifiable assets	15,114,882	13,712,359	$ 14,651,606
United States [Member]
Quarter ended:
Total revenues	1,396,361	942,803
Depreciation and amortization, net of (gains) losses on disposals	127,650	168,526
Interest expense	38,128	38,654
Pretax earnings (loss)	437,949	111,949
Income tax expense	105,302	25,783
Identifiable assets	14,661,722	13,279,882
Canada [Member]
Quarter ended:
Total revenues	76,495	44,434
Depreciation and amortization, net of (gains) losses on disposals	(1,540)	3,777
Interest expense	1,050	867
Pretax earnings (loss)	16,801	2,369
Income tax expense	4,273	809
Identifiable assets	$ 453,160	$ 432,477