Consolidated Statement Of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Consolidated Statement Of Income [Abstract]
Service revenues and sales	$ 360,182	$ 357,198	$ 718,482	$ 723,839
Cost of services provided and goods sold (excluding depreciation)	257,007	255,359	514,826	519,666
Selling, general and administrative expenses	53,649	53,107	109,320	108,667
Depreciation	7,272	6,899	14,421	13,694
Amortization	735	1,181	1,744	2,308
Other operating expenses		14,760		14,760
Total costs and expenses	318,663	331,306	640,311	659,095
Income from operations	41,519	25,892	78,171	64,744
Interest expense	(2,429)	(3,697)	(6,244)	(7,791)
Other income - net	756	1,696	1,572	3,402
Income before income taxes	39,846	23,891	73,499	60,355
Income taxes	(15,483)	(9,283)	(28,562)	(23,469)
Net income	$ 24,363	$ 14,608	$ 44,937	$ 36,886
Earnings Per Share
Net income	$ 1.41	$ 0.79	$ 2.59	$ 1.99
Average number of shares outstanding	17,236	18,606	17,374	18,564
Diluted Earnings Per Share
Net income	$ 1.36	$ 0.77	$ 2.48	$ 1.94
Average number of shares outstanding	17,880	18,966	18,097	18,980
Cash Dividends Per Share	$ 0.20	$ 0.18	$ 0.40	$ 0.36