Reinsurance (Income Statement Reinsurance Results) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Premiums:
Direct	$ 1,882,584	$ 1,807,809	$ 1,720,896
Assumed	206	230	194
Ceded	(1,854,246)	(1,757,231)	(1,666,384)
Net premiums	28,544	50,808	54,706
Policy charges and fee income:
Direct	3,725,113	3,248,574	3,459,134
Assumed	519,265	497,751	473,573
Ceded	(3,700,222)	(3,212,998)	(3,657,014)
Net policy charges and fee income	544,156	533,327	275,693
Net investment income:
Direct	398,762	330,058	356,291
Assumed	1,631	1,581	1,484
Ceded	(6,596)	(6,352)	(5,365)
Net investment income	393,797	325,287	352,410
Asset administration fees:
Direct	355,118	346,727	340,461
Assumed	0	0	0
Ceded	(339,062)	(332,359)	(322,868)
Net asset administration fees	16,056	14,368	17,593
Other income:
Direct	83,891	68,931	62,830
Assumed	(293)	96	390
Ceded	(59)	(55)	(77)
Amortization of reinsurance income	21	3,992	4,606
Net other income	83,560	72,964	67,749
Realized investment gains (losses), net:
Direct	(1,912,241)	769,114	478,117
Assumed	0	0	0
Ceded	1,795,492	(936,392)	(558,303)
Realized investment gains (losses), net	(116,749)	(167,278)	(80,186)
Policyholders’ benefits (including change in reserves):
Direct	3,352,159	2,647,574	2,436,537
Assumed	885,542	599,589	584,909
Ceded	(4,084,627)	(3,097,664)	(3,039,862)
Net policyholders’ benefits (including change in reserves)	153,074	149,499	(18,416)
Interest credited to policyholders’ account balances:
Direct	470,551	499,458	350,262
Assumed	135,355	141,307	135,123
Ceded	(418,677)	(468,772)	(316,994)
Net interest credited to policyholders’ account balances	187,229	171,993	168,391
Net reinsurance expense allowances, net of capitalization and amortization	(1,772,111)	(1,587,360)	(1,302,020)
Unaffiliated
Premiums:
Assumed	200	200	200
Ceded	(600)	(200)	(0)
Policy charges and fee income:
Ceded	(34,000)	(20,000)	(8,000)
Other income:
Assumed	(300)	100	400
Realized investment gains (losses), net:
Ceded	44,000	(34,000)	(20,000)
Policyholders’ benefits (including change in reserves):
Assumed	1,900	0	400
Ceded	$ (30,000)	$ (10,000)	$ 4,000