Basis Of Presentation (Narrative) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Lease right of use assets	$ 90,755,000		$ 90,755,000
Lease liabilities	$ 101,593,000		$ 101,593,000
Weighted average rate	3.46%		3.46%			3.47%
Effective tax rate	21.10%	4.70%	17.10%	12.20%
Excess tax benefit on stock options reduced income tax expense	$ 3,200,000	$ 11,700,000	$ 9,900,000	$ 15,500,000
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	$ 2,800,000		2,800,000
Capitalized contract cost, amortization expense			$ 0