Industry Segment and Geographic Area Data (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018
Quarter ended:
Total revenues	$ 1,019,577	$ 957,925
Depreciation and amortization, net of (gains) losses on disposals	132,458	133,003
Interest expense	35,254	30,345
Pretax earnings (loss)	169,197	198,686
Income tax expense	41,348	72,479
Identifiable assets	11,001,484	9,801,140	$ 10,747,422
United States [Member]
Quarter ended:
Total revenues	971,295	913,114
Depreciation and amortization, net of (gains) losses on disposals	131,379	131,499
Interest expense	34,549	29,643
Pretax earnings (loss)	163,262	191,973
Income tax expense	39,777	70,610
Identifiable assets	10,657,222	9,390,397
Canada [Member]
Quarter ended:
Total revenues	48,282	44,811
Depreciation and amortization, net of (gains) losses on disposals	1,079	1,504
Interest expense	705	702
Pretax earnings (loss)	5,935	6,713
Income tax expense	1,571	1,869
Identifiable assets	$ 344,262	$ 410,743