Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 571,577	$ 417,743	$ 438,873
Less: investment expenses	(20,029)	(14,935)	(16,064)
Net investment income	551,548	402,808	422,809
Equity securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	568	678	567
Commercial mortgage and other loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	51,628	51,040	48,598
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	630	737	1,069
Short-term investments and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	85,084	28,645	31,505
Other invested assets
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	34,422	13,733	20,626
Available-for-sale | Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	389,165	317,726	332,148
Trading | Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 10,080	$ 5,184	$ 4,360