Fair Value of Financial Instruments (Estimated Fair Values Of Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Assets
Investments	$ 2,880,003
Liabilities
Options sold	11,785	$ 4,219
Liabilities fair value	301,785	294,219
Level 2 [Member]
Liabilities
Liabilities fair value	301,525	294,025
Secured Debt [Member] | Borrowings [Member]
Liabilities
Liabilities fair value	140,000	140,000
Secured Debt [Member] | Borrowings [Member] | Level 2 [Member]
Liabilities
Liabilities fair value	140,000	140,000
Unsecured Debt [Member] | Borrowings [Member]
Liabilities
Liabilities fair value	150,000	150,000
Unsecured Debt [Member] | Borrowings [Member] | Level 2 [Member]
Liabilities
Liabilities fair value	150,000	150,000
Equity Contract [Member]
Liabilities
Equity contracts	11,525	4,025
Investments [Member]
Assets
Investments	3,380,642	3,403,822
Secured Debt [Member] | Secured Debt [Member] | Borrowings [Member] | Level 2 [Member]
Liabilities
Liabilities fair value		140,000
Other liabilities [Member] | Not Designated as Hedging Instrument [Member] | Equity Contract [Member]
Liabilities
Options sold	$ 260	$ 194