Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 99,827	$ 90,813	$ 307,551	$ 259,484
Less: investment expenses	(4,571)	(4,627)	(13,483)	(13,734)
Net investment income	95,256	86,186	294,068	245,750
Equity securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	222	222	664	664
Commercial mortgage and other loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	13,296	12,462	39,222	37,170
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	17,863	16,628	50,828	48,861
Short-term investments and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	2,440	952	6,590	1,389
Other invested assets
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	3,772	5,169	31,743	7,027
Available-for-sale | Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	61,889	55,109	177,525	163,564
Trading | Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 345	$ 271	$ 979	$ 809