Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Consolidated Statements Of Income [Abstract]
Service revenues and sales (Note 2)	$ 2,134,963	$ 2,139,261	$ 2,079,583
Cost of services provided and goods sold (excluding depreciation)	1,369,877	1,369,458	1,378,197
Selling, general and administrative expenses	358,727	366,727	330,218
Depreciation	49,102	49,011	46,596
Amortization	10,070	10,040	9,987
Other operating (income)/expenses (Note 20)	3,691	987	(75,095)
Total costs and expenses	1,791,467	1,796,223	1,689,903
Income from operations	343,496	343,038	389,680
Interest expense	(4,584)	(1,868)	(2,355)
Other (expense)/income--net (Note 10)	(9,233)	9,144	8,665
Income before income taxes	329,679	350,314	395,990
Income taxes (Note 11)	(80,055)	(81,764)	(76,524)
Net income	$ 249,624	$ 268,550	$ 319,466
Earnings Per Share (Note 16)
Net income	$ 16.72	$ 17.14	$ 20.02
Average number of shares outstanding	14,929	15,671	15,955
Diluted Earnings Per Share (Note 16)
Net income	$ 16.53	$ 16.85	$ 19.48
Average number of shares outstanding	15,099	15,938	16,398