Consolidated Statement Of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Consolidated Statement Of Income [Abstract]
Service revenues and sales	$ 381,921	$ 360,182	$ 758,573	$ 718,482
Cost of services provided and goods sold (excluding depreciation)	270,663	257,007	539,548	514,826
Selling, general and administrative expenses	57,994	53,649	116,582	109,320
Depreciation	8,082	7,272	16,114	14,421
Amortization	582	735	1,158	1,744
Total costs and expenses	337,321	318,663	673,402	640,311
Income from operations	44,600	41,519	85,171	78,171
Interest expense	(969)	(2,429)	(1,938)	(6,244)
Other income - net	536	756	1,099	1,572
Income before income taxes	44,167	39,846	84,332	73,499
Income taxes	(17,192)	(15,483)	(32,820)	(28,562)
Net income	$ 26,975	$ 24,363	$ 51,512	$ 44,937
Earnings Per Share
Net income	$ 1.60	$ 1.41	$ 3.05	$ 2.59
Average number of shares outstanding	16,880	17,236	16,872	17,374
Diluted Earnings Per Share
Net income	$ 1.55	$ 1.36	$ 2.96	$ 2.48
Average number of shares outstanding	17,419	17,880	17,419	18,097
Cash Dividends Per Share	$ 0.22	$ 0.20	$ 0.44	$ 0.40