Industry Segment and Geographic Area Data (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Mar. 31, 2016
Quarter ended:
Total revenues	$ 923,409	$ 884,805
Depreciation and amortization, net of (gains) losses on disposals	103,323	55,760
Interest expense	26,644	22,100
Pretax earnings (loss)	233,131	269,008
Income tax expense	85,958	97,723
Identifiable assets	8,543,809	7,090,634	$ 8,127,363
United States [Member]
Quarter ended:
Total revenues	880,947	841,463
Depreciation and amortization, net of (gains) losses on disposals	102,000	56,739
Interest expense	26,644	21,989
Pretax earnings (loss)	224,913	259,127
Income tax expense	83,745	95,095
Identifiable assets	8,269,109	6,874,093
Canada [Member]
Quarter ended:
Total revenues	42,462	43,342
Depreciation and amortization, net of (gains) losses on disposals	1,323	(979)
Interest expense		111
Pretax earnings (loss)	8,218	9,881
Income tax expense	2,213	2,628
Identifiable assets	$ 274,700	$ 216,541