Industry Segment and Geographic Area Data (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2015
Quarter ended:
Total revenues	$ 884,805	$ 818,955
Depreciation and amortization, net of (gains) losses on disposals	55,760	65,235
Interest expense	22,100	24,148
Pretax earnings (loss)	269,008	195,051
Income tax expense	97,723	70,577
Identifiable assets	7,090,634	6,528,682	$ 6,872,175
United States [Member]
Quarter ended:
Total revenues	841,463	773,043
Depreciation and amortization, net of (gains) losses on disposals	56,739	64,040
Interest expense	21,989	24,019
Pretax earnings (loss)	259,127	186,907
Income tax expense	95,095	68,419
Identifiable assets	6,874,093	6,358,303
Canada [Member]
Quarter ended:
Total revenues	43,342	45,912
Depreciation and amortization, net of (gains) losses on disposals	(979)	1,195
Interest expense	111	129
Pretax earnings (loss)	9,881	8,144
Income tax expense	2,628	2,158
Identifiable assets	$ 216,541	$ 170,379