Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Consolidated Statements Of Income [Abstract]
Service revenues and sales	$ 526,472	$ 538,667	$ 1,588,309	$ 1,598,283
Cost of services provided and goods sold (excluding depreciation)	346,934	342,164	1,020,307	1,033,130
Selling, general and administrative expenses	83,992	89,217	261,799	274,654
Depreciation	12,154	11,844	37,006	37,171
Amortization	2,520	2,510	7,558	7,530
Other operating expense/(income)	15	63	(530)	789
Total costs and expenses	445,615	445,798	1,326,140	1,353,274
Income from operations	80,857	92,869	262,169	245,009
Interest expense	(1,271)	(583)	(2,983)	(1,343)
Other (expense)/income - net	(3,115)	3,134	(11,907)	10,521
Income before income taxes	76,471	95,420	247,279	254,187
Income taxes	(19,598)	(23,417)	(59,781)	(60,262)
Net income	$ 56,873	$ 72,003	$ 187,498	$ 193,925
Earnings Per Share:
Net income	$ 3.82	$ 4.62	$ 12.55	$ 12.27
Average number of shares outstanding	14,888	15,587	14,935	15,808
Diluted Earnings Per Share:
Net income	$ 3.78	$ 4.55	$ 12.41	$ 12.06
Average number of shares outstanding	15,042	15,842	15,114	16,083
Cash Dividends Per Share	$ 0.38	$ 0.36	$ 1.10	$ 1.04