Investments in Fixed Maturity Securities (HTM Allowance for Credit Loss) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020	$ (948)	$ 0
Cumulative effect adjustment resulting from changes in accounting principles	871	871
Provision for expected credit losses	(77)	802
Allowance for expected credit losses at September 30, 2020	$ 871	871
Cumulative effect adjustment resulting from changes in accounting principles
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020		69
Cumulative effect adjustment resulting from changes in accounting principles		$ 69