Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Consolidated Statements Of Income [Abstract]
Service revenues and sales	$ 502,199	$ 473,584	$ 1,017,997	$ 935,618
Cost of services provided and goods sold (excluding depreciation)	352,163	323,637	703,908	645,588
Selling, general and administrative expenses	84,513	71,556	155,096	145,585
Depreciation	11,659	9,887	23,047	19,597
Amortization	2,488	406	4,965	925
Other operating (income)/expenses	(41,384)	2,570	(41,142)	8,923
Total costs and expenses	409,439	408,056	845,874	820,618
Income from operations	92,760	65,528	172,123	115,000
Interest expense	(651)	(1,237)	(1,626)	(2,361)
Other (expense)/income - net	7,514	13	(1,952)	2,452
Income before income taxes	99,623	64,304	168,545	115,091
Income taxes	(17,522)	(13,575)	(30,553)	(19,695)
Net income	$ 82,101	$ 50,729	$ 137,992	$ 95,396
Earnings Per Share:
Net income	$ 5.16	$ 3.18	$ 8.65	$ 5.98
Average number of shares outstanding	15,914	15,928	15,953	15,941
Diluted Earnings Per Share:
Net income	$ 5.01	$ 3.08	$ 8.39	$ 5.79
Average number of shares outstanding	16,373	16,449	16,445	16,489
Cash Dividends Per Share	$ 0.32	$ 0.30	$ 0.64	$ 0.60