Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 98,970	$ 99,827	$ 271,323	$ 307,551
Less: investment expenses	(4,978)	(4,571)	(14,288)	(13,483)
Net investment income	93,992	95,256	257,035	294,068
Equity securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	102	222	307	664
Commercial mortgage and other loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	11,921	13,296	38,019	39,222
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	17,716	17,863	52,642	50,828
Other invested assets
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	13,890	3,772	12,146	31,743
Short-term investments and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	376	2,440	2,988	6,590
Available-for-sale | Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	54,494	61,889	163,957	177,525
Trading | Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 471	$ 345	$ 1,264	$ 979