Investments (Fair Value Below Amortized Cost of Gross Unrealized Losses for Fixed Maturity Securities) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Gross unrealized losses with number of securities [Line Items]
Document Period End Date	Sep. 30, 2019
Gross Unrealized Losses	$ 102,243	$ 748,490
% of Total	100.00%	100.00%
Less than 20%
Gross unrealized losses with number of securities [Line Items]
Gross Unrealized Losses	$ 75,658	$ 721,015
% of Total	74.00%	96.30%
20% or more for less than six months
Gross unrealized losses with number of securities [Line Items]
Gross Unrealized Losses	$ 10,064	$ 21,336
% of Total	9.80%	2.90%
20% or more for six months or greater
Gross unrealized losses with number of securities [Line Items]
Gross Unrealized Losses	$ 16,521	$ 6,139
% of Total	16.20%	0.80%