Investments (Fair Value Below Amortized Cost of Gross Unrealized Losses for Fixed Maturity and Equity Securities) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Gross unrealized losses with number of securities [Line Items]
Gross Unrealized Losses	$ 230,223	$ 748,490
% of Total	100.00%	100.00%
Less than 20%
Gross unrealized losses with number of securities [Line Items]
Gross Unrealized Losses	$ 208,034	$ 721,015
% of Total	90.30%	96.30%
20% or more for less than six months
Gross unrealized losses with number of securities [Line Items]
Gross Unrealized Losses	$ 20,845	$ 21,336
% of Total	9.10%	2.90%
20% or more for six months or greater
Gross unrealized losses with number of securities [Line Items]
Gross Unrealized Losses	$ 1,344	$ 6,139
% of Total	0.60%	0.80%