Reinsurance (Reinsurance amounts included in the Statements of Financial Position) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Effects of Reinsurance [Line Items]
Reinsurance recoverables	$ 487,748	$ 563,428
Deferred policy acquisition costs	4,431,765	4,596,565
Deferred sales inducements	907,575	1,020,786
Value of business acquired	(34,967)	(35,109)
Other assets	116,861	121,086
Policyholders’ account balances	5,062,233	4,846,152
Future policy benefits	5,984,878	9,132,569
Reinsurance payables	214,420	262,588
Other liabilities	395,657	422,636
Impacts of Reinsurance
Effects of Reinsurance [Line Items]
Reinsurance recoverables	487,748	563,428
Deferred policy acquisition costs	3,684,641	3,766,066
Deferred sales inducements	484,204	540,389
Value of business acquired	(2,561)	(2,702)
Other assets	100,053	105,167
Policyholders’ account balances	3,029,531	2,825,030
Future policy benefits	3,269,692	5,511,496
Reinsurance payables	214,420	262,588
Other liabilities	296,686	329,019
Unaffiliated activity
Effects of Reinsurance [Line Items]
Reinsurance recoverables	0	300
Reinsurance payables	$ 100	$ 100