Industry Segment and Geographic Area Data (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2019
Quarter ended:
Total revenues	$ 1,079,249	$ 1,019,577
Depreciation and amortization, net of (gains) losses on disposals	145,042	132,458
Pretax earnings (loss)	174,714	169,197
Identifiable assets	12,474,744	11,001,484	$ 11,891,713
United States [Member]
Quarter ended:
Total revenues	1,028,574	971,295
Depreciation and amortization, net of (gains) losses on disposals	141,898	131,379
Interest expense	38,220	34,549
Pretax earnings (loss)	170,847	163,262
Income tax expense	41,114	39,777
Identifiable assets	12,076,714	10,657,222
Canada [Member]
Quarter ended:
Total revenues	50,675	48,282
Depreciation and amortization, net of (gains) losses on disposals	3,144	1,079
Interest expense	668	705
Pretax earnings (loss)	3,867	5,935
Income tax expense	1,178	1,571
Identifiable assets	$ 398,030	$ 344,262