Income Taxes (Reconciliation To Effective Rate) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Expected federal income tax expense	$ 59,591	$ 112,472	$ 174,077
Non-taxable investment income	(157,408)	(146,324)	(161,407)
Tax credits	(29,506)	(30,916)	(24,232)
Domestic production activities deduction, net	(10,448)	(9,488)	0
Changes in tax law	(17,576)	0	0
Other	693	387	921
Total income tax expense (benefit)	$ (154,654)	$ (73,869)	$ (10,641)
Effective tax rate	(90.80%)	(22.90%)	(2.10%)