Industry Segment and Geographic Area Data (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Mar. 31, 2019
Quarter ended:
Total revenues	$ 1,150,214	$ 1,104,507	$ 2,229,463	$ 2,124,084
Depreciation and amortization, net of (gains) losses on disposals	157,851	138,534	302,893	270,992
Pretax earnings (loss)	205,354	215,660	380,068	384,857
Identifiable assets	12,856,202	11,323,845	12,856,202	11,323,845	$ 11,891,713
United States [Member]
Quarter ended:
Total revenues	1,092,762	1,049,846	2,121,336	2,021,141
Depreciation and amortization, net of (gains) losses on disposals	154,968	137,537	296,866	268,916
Interest expense	38,261	34,324	76,481	68,873
Pretax earnings (loss)	200,112	208,208	370,959	371,470
Income tax expense	47,534	50,107	88,648	89,884
Identifiable assets	12,441,917	10,963,411	12,441,917	10,963,411
Canada [Member]
Quarter ended:
Total revenues	57,452	54,661	108,127	102,943
Depreciation and amortization, net of (gains) losses on disposals	2,883	997	6,027	2,076
Interest expense	861	706	1,529	1,411
Pretax earnings (loss)	5,242	7,452	9,109	13,387
Income tax expense	1,494	2,011	2,672	3,582
Identifiable assets	$ 414,285	$ 360,434	$ 414,285	$ 360,434