Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Consolidated Statements Of Income [Abstract]
Service revenues and sales	$ 462,034	$ 439,176
Cost of services provided and goods sold (excluding depreciation)	321,951	304,536
Selling, general and administrative expenses	74,029	69,000
Depreciation	9,710	9,267
Amortization	519	27
Other operating expenses/(income)	6,353	(51)
Total costs and expenses	412,562	382,779
Income from operations	49,472	56,397
Interest expense	(1,124)	(1,207)
Other income - net	2,439	1,018
Income before income taxes	50,787	56,208
Income taxes	(6,120)	(11,212)
Net income	$ 44,667	$ 44,996
Earnings Per Share:
Net income	$ 2.80	$ 2.79
Average number of shares outstanding	15,954	16,100
Diluted Earnings Per Share:
Net income	$ 2.70	$ 2.66
Average number of shares outstanding	16,525	16,887
Cash Dividends Per Share	$ 0.30	$ 0.28