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	$ 411,900	$ 343,452	$ 372,397
Less: investment expenses	(18,103)	(18,165)	(19,987)
Net investment income	393,797	325,287	352,410
Equity securities, at fair value
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income	856	885	884
Commercial mortgage and other loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income	57,886	49,577	52,127
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income	68,485	66,305	63,884
Short-term investments and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income	9,266	2,382	1,090
Other Invested Assets
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income	38,577	2,256	23,518
Available-for-sale Securities | Fixed Maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income	235,456	220,942	230,060
Trading | Fixed Maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income	$ 1,374	$ 1,105	$ 834