Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Consolidated Statements Of Income [Abstract]
Service revenues and sales	$ 595,880	$ 553,816	$ 1,185,113	$ 1,113,973
Cost of services provided and goods sold (excluding depreciation)	389,750	374,193	774,877	744,898
Selling, general and administrative expenses	102,255	94,987	218,128	195,082
Depreciation	13,167	12,634	26,454	24,920
Amortization	2,546	2,514	5,067	5,027
Other operating expense/(income)	37	(18)	129	1,721
Total costs and expenses	507,755	484,310	1,024,655	971,648
Income from operations	88,125	69,506	160,458	142,325
Interest expense	(429)	(771)	(854)	(2,322)
Other income - net	6,132	1,609	18,709	1,506
Income before income taxes	93,828	70,344	178,313	141,509
Income taxes	(22,941)	(16,967)	(42,409)	(34,011)
Net income	$ 70,887	$ 53,377	$ 135,904	$ 107,498
Earnings Per Share:
Net income	$ 4.70	$ 3.54	$ 8.99	$ 7.16
Average number of shares outstanding	15,097	15,058	15,109	15,013
Diluted Earnings Per Share:
Net income	$ 4.65	$ 3.51	$ 8.89	$ 7.09
Average number of shares outstanding	15,251	15,219	15,295	15,167
Cash Dividends Per Share	$ 0.40	$ 0.38	$ 0.80	$ 0.76