Consolidated Statement Of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Consolidated Statement Of Income [Abstract]
Service revenues and sales	$ 340,886	$ 354,353	$ 1,064,725	$ 1,061,466
Cost of services provided and goods sold (excluding depreciation)	243,184	256,610	762,850	771,423
Selling, general and administrative expenses	48,870	52,955	157,537	155,892
Depreciation	6,971	6,557	20,665	19,178
Amortization	1,190	1,135	3,498	3,375
Other operating expenses	11,461	1,126	26,221	1,126
Total costs and expenses	311,676	318,383	970,771	950,994
Income from operations	29,210	35,970	93,954	110,472
Interest expense	(3,500)	(3,743)	(11,291)	(11,032)
Other income/(expense) - net	(90)	1,840	3,312	2,965
Income/(loss) before income taxes	25,620	34,067	85,975	102,405
Income taxes	(8,188)	(13,222)	(31,657)	(39,841)
Net income	$ 17,432	$ 20,845	$ 54,318	$ 62,564
Earnings Per Share
Net income	$ 0.96	$ 1.10	$ 2.95	$ 3.30
Average number of shares outstanding	18,184	18,960	18,436	18,977
Diluted Earnings Per Share
Net income	$ 0.94	$ 1.07	$ 2.89	$ 3.23
Average number of shares outstanding	18,522	19,404	18,824	19,382
Cash Dividends Per Share	$ 0.20	$ 0.18	$ 0.56	$ 0.50