Consolidated Statement Of Income (USD $) In Thousands, except Per Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Consolidated Statement Of Income [Abstract]
Service revenues and sales	$ 341,439	$ 320,451	$ 1,005,717	$ 944,259
Cost of services provided and goods sold (excluding depreciation)	245,063	227,915	722,118	670,754
Selling, general and administrative expenses	47,618	48,200	153,696	146,694
Depreciation	6,313	6,385	18,959	18,048
Amortization	1,134	1,196	3,243	3,707
Total costs and expenses	300,128	283,696	898,016	839,203
Income from operations	41,311	36,755	107,701	105,056
Interest expense	(3,555)	(2,995)	(10,260)	(8,946)
Other income/(expense) - net	(1,935)	222	881	418
Income before income taxes	35,821	33,982	98,322	96,528
Income taxes	(13,934)	(12,994)	(38,048)	(37,327)
Net income	$ 21,887	$ 20,988	$ 60,274	$ 59,201
Earnings Per Share
Net income	$ 1.06	$ 0.93	$ 2.88	$ 2.62
Average number of shares outstanding	20,674	22,597	20,934	22,604
Diluted Earnings Per Share
Net income	$ 1.04	$ 0.91	$ 2.82	$ 2.57
Average number of shares outstanding	21,055	22,996	21,400	23,006
Cash Dividends Per Share	$ 0.16	$ 0.14	$ 0.44	$ 0.38