Investments in Fixed Maturity Securities (HTM Allowance for Credit Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at December 31, 2020	$ 798	$ 0
Cumulative effect adjustment resulting from changes in accounting principles	730	107
Provision for expected credit losses	(68)	38
Allowance for expected credit losses at March 31, 2021	$ 730	107
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 December 31, 2020		69
Cumulative effect adjustment resulting from changes in accounting principles		$ 69