Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 100,681	$ 88,077	$ 204,933	$ 172,353
Less: investment expenses	(5,381)	(4,615)	(10,766)	(9,310)
Net investment income	95,300	83,462	194,167	163,043
Equity securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	102	103	205	205
Commercial mortgage and other loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	13,322	12,322	26,748	26,098
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	17,315	17,615	34,349	34,926
Other invested assets
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	5,735	2,165	18,808	(1,744)
Short-term investments and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	33	580	160	2,612
Available-for-sale | Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	63,630	54,897	123,588	109,463
Trading | Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 544	$ 395	$ 1,075	$ 793