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 Net Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income, operating		$ 39,234	$ 37,661	$ 109,509	$ 113,443
Investment expenses		(1,577)	(2,217)	(6,176)	(6,576)
Investment income net of investment expenses		37,657	35,444	103,333	106,867
Interest expense on surplus note		(14,704)	(12,769)	(42,250)	(35,212)
Net investment income		22,953	22,675	61,083	71,655
Equity Securities [Member]
Schedule of Net Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income, operating		433	448	1,345	1,381
Policy Loans and Other Invested Assets [Member]
Schedule of Net Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income, operating		242	234	973	854
Cash and Cash Equivalents [Member]
Schedule of Net Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income, operating		114	1,191	1,099	3,808
Total return on deposit asset underlying 10% insurance agreement [Member]
Schedule of Net Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income, operating	[1]	2,858	2,639	1,962	11,130
Available-for-Sale [Member] | Fixed Maturities
Schedule of Net Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income, operating		20,883	20,380	61,880	61,058
Held-to-Maturity [Member] | Fixed Maturities
Schedule of Net Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income, operating		$ 14,704	$ 12,769	$ 42,250	$ 35,212

[1] ^{For the three and nine months ended September 30, 2020, included $1.2 million and $(2.9) million, respectively, of net gains (losses) recognized for the change in fair value of the deposit asset underlying the 10% coinsurance agreement.  For the three and nine months ended September 30, 2019, included $0.5 million and $5.1 million, respectively, of net gains recognized for the change in fair value of the deposit asset underlying the 10% coinsurance agreement.}