Industry Segment and Geographic Area Data (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Mar. 31, 2013
Quarter ended:
Total revenues	$ 746,831	$ 667,676
Depreciation and amortization, net of (gains) losses on disposals	61,117	58,936
Interest expense	23,328	23,491
Pretax earnings	179,048	127,388
Income tax expense	66,080	46,819
Identifiable assets	5,578,762	4,838,836	5,306,601
United States
Quarter ended:
Total revenues	703,963	626,183
Depreciation and amortization, net of (gains) losses on disposals	59,170	56,963
Interest expense	23,186	23,339
Pretax earnings	171,756	119,384
Income tax expense	64,148	44,698
Identifiable assets	5,425,667	4,690,153
Canada
Quarter ended:
Total revenues	42,868	41,493
Depreciation and amortization, net of (gains) losses on disposals	1,947	1,973
Interest expense	142	152
Pretax earnings	7,292	8,004
Income tax expense	1,932	2,121
Identifiable assets	$ 153,095	$ 148,683