Industry Segment and Geographic Area Data (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Mar. 31, 2017
Quarter ended:
Total revenues	$ 957,925	$ 923,191
Depreciation and amortization, net of (gains) losses on disposals	133,003	103,323
Interest expense	30,345	26,426
Pretax earnings (loss)	198,686	233,131
Income tax expense	72,479	85,958
Identifiable assets	9,801,140	8,543,809	$ 9,405,840
United States [Member]
Quarter ended:
Total revenues	913,114	880,729
Depreciation and amortization, net of (gains) losses on disposals	131,499	102,000
Interest expense	29,643	26,426
Pretax earnings (loss)	191,973	224,913
Income tax expense	70,610	83,745
Identifiable assets	9,390,397	8,269,109
Canada [Member]
Quarter ended:
Total revenues	44,811	42,462
Depreciation and amortization, net of (gains) losses on disposals	1,504	1,323
Interest expense	702
Pretax earnings (loss)	6,713	8,218
Income tax expense	1,869	2,213
Identifiable assets	$ 410,743	$ 274,700