Reinsurance (Effect of Reinsurance on Net Premiums and Claims and Other Policy Benefits) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Premiums Earned, Net [Abstract]
Direct Premiums Earned	$ 62,526	$ 61,571	$ 57,562
Assumed Premiums Earned	11,341,284	10,642,462	10,049,587
Ceded Premiums Earned	(860,034)	(862,903)	(858,278)
Net premiums	10,543,776	9,841,130	9,248,871
Policyholder Benefits and Claims Incurred, Net [Abstract]
Policyholder Benefits and Claims Incurred, Direct	107,405	104,447	105,435
Policyholder Benefits and Claims Incurred, Assumed	9,997,173	9,281,590	8,621,647
Policyholder Benefits and Claims Incurred, Ceded	(785,649)	(867,120)	(733,707)
Claims and other policy benefits	$ 9,318,929	$ 8,518,917	$ 7,993,375