Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 110,017	$ 86,177	$ 207,724	$ 168,671
Less: investment expenses	(4,455)	(4,528)	(8,912)	(9,107)
Net investment income	105,562	81,649	198,812	159,564
Equity securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	221	221	442	442
Commercial mortgage and other loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	13,435	12,303	25,926	24,708
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	16,766	16,329	32,965	32,233
Short-term investments and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	1,839	114	4,150	437
Other invested assets
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	18,060	1,743	27,971	1,858
Available-for-sale | Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	59,370	55,195	115,636	108,455
Trading | Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 326	$ 272	$ 634	$ 538