Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Consolidated Statements Of Income [Abstract]
Service revenues and sales (Note 2)	$ 2,264,417	$ 2,134,963	$ 2,139,261
Cost of services provided and goods sold (excluding depreciation)	1,465,602	1,369,877	1,369,458
Selling, general and administrative expenses	395,120	358,727	366,727
Depreciation	50,802	49,102	49,011
Amortization	10,063	10,070	10,040
Other operating expenses (Note 20)	2,261	3,691	987
Total costs and expenses	1,923,848	1,791,467	1,796,223
Income from operations	340,569	343,496	343,038
Interest expense	(3,108)	(4,584)	(1,868)
Other income/(expense)--net (Note 10)	12,906	(9,233)	9,144
Income before income taxes	350,367	329,679	350,314
Income taxes (Note 11)	(77,858)	(80,055)	(81,764)
Net income	$ 272,509	$ 249,624	$ 268,550
Earnings Per Share (Note 16)
Net income	$ 18.11	$ 16.72	$ 17.14
Average number of shares outstanding	15,050	14,929	15,671
Diluted Earnings Per Share (Note 16)
Net income	$ 17.93	$ 16.53	$ 16.85
Average number of shares outstanding	15,200	15,099	15,938