Industry Segment and Geographic Area Data (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Mar. 31, 2012
Quarter ended:
Total revenues	$ 665,416	$ 642,965
Depreciation and amortization, net of (gains) losses on disposals	58,936	48,733
Interest expense	23,491	22,633
Pretax earnings	127,388	125,730
Income tax expense	46,819	47,507
Identifiable assets	4,838,836	4,174,456	4,654,051
United States
Quarter ended:
Total revenues	623,923	601,091
Depreciation and amortization, net of (gains) losses on disposals	56,963	46,864
Interest expense	23,339	22,470
Pretax earnings	119,384	118,357
Income tax expense	44,698	45,329
Identifiable assets	4,690,153	4,026,330
Canada
Quarter ended:
Total revenues	41,493	41,874
Depreciation and amortization, net of (gains) losses on disposals	1,973	1,869
Interest expense	152	163
Pretax earnings	8,004	7,373
Income tax expense	2,121	2,178
Identifiable assets	$ 148,683	$ 148,126