Reinsurance (Reinsurance amounts included in the Statements of Financial Position) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Effects of Reinsurance [Line Items]
Reinsurance recoverables	$ 592,751	$ 572,102
Deferred policy acquisition costs	4,496,083	4,447,505
Deferred sales inducements	881,464	889,598
Value of business acquired	33,012	33,222
Other assets	101,856	85,310
Policyholders’ account balances	5,465,749	5,353,596
Future policy benefits	10,346,448	9,368,986
Reinsurance payables	268,835	232,937
Other liabilities	406,009	811,016
Impacts of Reinsurance
Effects of Reinsurance [Line Items]
Reinsurance recoverables	592,751	572,102
Deferred policy acquisition costs	3,762,300	3,703,166
Deferred sales inducements	481,564	476,608
Value of business acquired	(2,425)	(2,431)
Other assets	90,099	79,992
Policyholders’ account balances	3,132,527	3,098,537
Future policy benefits	6,439,923	5,680,939
Reinsurance payables	268,835	232,937
Other liabilities	299,065	290,330
Unaffiliated activity
Effects of Reinsurance [Line Items]
Reinsurance recoverables	200	0
Reinsurance payables	$ 100	$ 100