Acquisitions (Schedule Of Business Acquisitions Pro Forma Of Operations) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Acquisitions [Abstract]
Service revenues and sales	$ 500,108	$ 472,090	$ 1,479,859	$ 1,420,535
Net income	$ 62,154	$ 56,408	$ 164,562	$ 166,640
Earnings per share	$ 3.89	$ 3.51	$ 10.32	$ 10.37
Diluted earnings per share	$ 3.75	$ 3.36	$ 9.96	$ 9.90