Basis Of Presentation (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) item	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) item	Sep. 30, 2018 USD ($)	Mar. 31, 2019 USD ($)	Jan. 01, 2019	Dec. 31, 2018 USD ($)
Lease right of use assets	$ 103,286,000		$ 103,286,000
Lease liabilities	$ 115,773,000		$ 115,773,000
Weighted average rate	3.38%		3.38%			3.47%
Number of cloud computing arrangements | item	2		2
Effective tax rate	11.90%	18.60%	15.20%	14.50%
Excess tax benefit on stock options reduced income tax expense	$ 8,800,000	$ 3,100,000	$ 18,700,000	$ 18,600,000
Capitalized property and equipment	1,100,000		1,100,000				$ 3,200,000
ASU 2016-02 [Member]
Lease right of use assets					$ 87,800,000
Lease liabilities					$ 98,700,000
Weighted average rate						3.47%
Cloud Computing [Member] | ASU No. 2018-15 [Member]
Capitalized contract cost	$ 4,800,000		4,800,000
Capitalized contract cost, amortization expense			$ 0