Industry Segment and Geographic Area Data (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Mar. 31, 2015
Quarter ended:
Total revenues	$ 744,751	$ 706,355	$ 2,592,459	$ 2,431,801
Depreciation and amortization, net of (gains) losses on disposals	90,851	86,532	215,332	223,123
Interest expense	25,407	25,719	71,480	74,744
Pretax earnings	132,495	107,433	688,598	549,362
Income tax expense	50,726	40,893	252,165	202,101
Identifiable assets	7,762,534	6,906,532	7,762,534	6,906,532	$ 6,872,175
United States [Member]
Quarter ended:
Total revenues	713,416	671,311	2,470,785	2,297,289
Depreciation and amortization, net of (gains) losses on disposals	90,273	85,038	215,995	218,923
Interest expense	25,357	25,580	71,319	74,347
Pretax earnings	128,799	104,830	664,189	529,537
Income tax expense	49,776	40,203	245,797	196,847
Identifiable assets	7,534,725	6,715,544	7,534,725	6,715,544
Canada [Member]
Quarter ended:
Total revenues	31,335	35,044	121,674	134,512
Depreciation and amortization, net of (gains) losses on disposals	578	1,494	(663)	4,200
Interest expense	50	139	161	397
Pretax earnings	3,696	2,603	24,409	19,825
Income tax expense	950	690	6,368	5,254
Identifiable assets	$ 227,809	$ 190,988	$ 227,809	$ 190,988