Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Consolidated Statements Of Income [Abstract]
Service revenues and sales	$ 553,816	$ 531,288	$ 1,113,973	$ 1,061,837
Cost of services provided and goods sold (excluding depreciation)	374,193	336,821	744,898	673,373
Selling, general and administrative expenses	94,987	87,853	195,082	177,807
Depreciation	12,634	12,714	24,920	24,852
Amortization	2,514	2,520	5,027	5,038
Other operating expense/(income)	(18)	(558)	1,721	(545)
Total costs and expenses	484,310	439,350	971,648	880,525
Income from operations	69,506	91,938	142,325	181,312
Interest expense	(771)	(902)	(2,322)	(1,712)
Other expense/(income) - net	1,609	(4,930)	1,506	(8,792)
Income before income taxes	70,344	86,106	141,509	170,808
Income taxes	(16,967)	(19,650)	(34,011)	(40,183)
Net income	$ 53,377	$ 66,456	$ 107,498	$ 130,625
Earnings Per Share:
Net income	$ 3.54	$ 4.45	$ 7.16	$ 8.73
Average number of shares outstanding	15,058	14,932	15,013	14,959
Diluted Earnings Per Share:
Net income	$ 3.51	$ 4.40	$ 7.09	$ 8.62
Average number of shares outstanding	15,219	15,111	15,167	15,152
Cash Dividends Per Share	$ 0.38	$ 0.36	$ 0.76	$ 0.72