Financial Instruments (Estimated Fair Values Of Financial Instruments) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Investments [Member]
Assets
Assets	$ 4,946,202	$ 4,729,270
Financing Receivable [Member]
Assets
Assets	5,712	5,725
Fair Value, Measurements, Recurring [Member]
Liabilities
Liabilities	81
Fair Value, Measurements, Recurring [Member] | Call Option [Member]
Liabilities
Liabilities	$ 81	$ 0