Fair Value Measurements (Summary Of Quantitative Information About Level 3 Fair Value Measurements) (Details)	3 Months Ended
	Mar. 31, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Valuation Technique, Discounted cash flow	Discounted cash flow
Auction Rate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Valuation Technique, Discounted cash flow	Discounted cash flow
Unobservable Input, Estimated market recovery period	5 years
Auction Rate Securities [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Unobservable Input, Estimated market rate	5.70%
Auction Rate Securities [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Unobservable Input, Estimated market rate	6.50%
Auction Rate Securities [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Unobservable Input, Estimated market recovery period	5 years	[1]
Unobservable Input, Estimated market rate	5.80%	[1]
Private Equity Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Valuation Technique, Market comparable companies	Market comparable companies
Private Equity Investments [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value inputs, Earnings before interest, taxes, depreciation, amortization (EBITDA) multiple	4.0
Private Equity Investments [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value inputs, Earnings before interest, taxes, depreciation, amortization (EBITDA) multiple	6.0
Private Equity Investments [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value inputs, Earnings before interest, taxes, depreciation, amortization (EBITDA) multiple	5.3	[1]

[1] * Unobservable inputs were weighted by the relative fair value of the instruments.