Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Jan. 01, 2018	Jan. 01, 2017
Securities loaned
Cash collateral received as percentage of fair value of securities loaned		102.00%
Cash collateral received for securities loaned percentage foreign		105.00%
Deferred policy acquisition and sales inducement costs
Present value of future profits		$ 3,000	$ 3,000
Amortization expense of future profits		$ 357	$ 249	$ 232
Cumulative effect of change in accounting principle							$ 0
Minimum
Deferred policy acquisition and sales inducement costs
Period for amortization of DAC and DSI for interest-sensitive life, fixed annuities and other investment contracts		15 years
Maximum
Securities loaned
Length of securities lending transaction period		30 days
Deferred policy acquisition and sales inducement costs
Period for amortization of DAC and DSI for interest-sensitive life, fixed annuities and other investment contracts		30 years
Interest-sensitive life insurance | Minimum
Deferred policy acquisition and sales inducement costs
Period for amortization of DAC and DSI for interest-sensitive life, fixed annuities and other investment contracts		10 years
Interest-sensitive life insurance | Maximum
Deferred policy acquisition and sales inducement costs
Period for amortization of DAC and DSI for interest-sensitive life, fixed annuities and other investment contracts		20 years
Fixed annuities | Minimum
Deferred policy acquisition and sales inducement costs
Period for amortization of DAC and DSI for interest-sensitive life, fixed annuities and other investment contracts		5 years
Fixed annuities | Maximum
Deferred policy acquisition and sales inducement costs
Period for amortization of DAC and DSI for interest-sensitive life, fixed annuities and other investment contracts		10 years
Accounting Standards Update 2016-01
Deferred policy acquisition and sales inducement costs
Equity securities						$ (308,000)
Private equity/debt funds, real estate funds and tax credit funds
Deferred policy acquisition and sales inducement costs
Period over which recognition of income on funds is delayed		3 months
Retained income
Deferred policy acquisition and sales inducement costs
Cumulative effect of change in accounting principle					$ 0	$ 314,000	$ 0
Forecast [Member] | Retained income | Accounting Standards Update 2016-13 | Maximum
Deferred policy acquisition and sales inducement costs
Allowance for credit loss, period increase (decrease)	$ 85,000
Cumulative effect of change in accounting principle	$ (55,000)