Business Acquisition Business Acquisitions (Supplementary Information On Unaudited Pro Forma Financial Results Of Acquisition) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
2018 Business Acquisition [Member]
Business Acquisition, Pro Forma Revenue	$ 1,264,544	$ 1,218,530
Business Acquisition, Pro Forma Net Income (Loss)	$ 121,727	$ 123,378
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 2.50	$ 2.56
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 2.45	$ 2.50
2016 Business Acquisition [Member]
Business Acquisition, Pro Forma Revenue			$ 1,102,510	$ 1,009,169
Business Acquisition, Pro Forma Net Income (Loss)			$ 108,822	$ 111,817
Business Acquisition, Pro Forma Earnings Per Share, Basic			$ 2.25	$ 2.31
Business Acquisition, Pro Forma Earnings Per Share, Diluted			$ 2.24	$ 2.29
EVDY [Member]
Business Acquisition, Pro Forma Revenue			$ 1,082,813	$ 952,806
Business Acquisition, Pro Forma Net Income (Loss)			$ 103,541	$ 115,059
Business Acquisition, Pro Forma Earnings Per Share, Basic			$ 2.14	$ 2.38
Business Acquisition, Pro Forma Earnings Per Share, Diluted			$ 2.13	$ 2.35