Investment Operations Net Unrealized Gains (Losses) on Investments in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Unrealized Gains Losses [Line Items]
Assumed changes in amortization of DAC	$ 200,227	$ 46,732
Impact of net unrealized investment gains and losses	12,498	6,878	$ 14,870
Assumed changes in amortization patter of URR	18,025	5,134
Assumed changes in policyholder liability	(30,642)	(1,642)
Provision for deferred income taxes	97,023	26,596
Accumulated net unrealized investment gain (loss)
Net Unrealized Gains Losses [Line Items]
Net Unrealized gains losses on investments in Accumulated other comprehensive Income	364,994	100,054
Debt Securities
Net Unrealized Gains Losses [Line Items]
Available-for-sale Securities, Accumulated Gross Unrealized Gain (Loss), before Tax	$ 687,359	$ 176,768