Investment Operations Net Unrealized Gains (Losses) on Investments in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Unrealized Gains Losses [Line Items]
Assumed changes in amortization of DAC	$ 95,647	$ 73,735
Impact of net unrealized investment gains and losses	12,382	3,087	$ 3,939
Assumed changes in amortization patter of URR	4,215	3,352
Assumed changes in policyholder liability	(3,795)	(4,090)
Provision for deferred income taxes	84,684	64,955
Debt Securities [Member]
Net Unrealized Gains Losses [Line Items]
Available-for-sale Securities, Accumulated Gross Unrealized Gain (Loss), before Tax	347,079	257,857
Equity Securities [Member]
Net Unrealized Gains Losses [Line Items]
Available-for-sale Securities, Accumulated Gross Unrealized Gain (Loss), before Tax	2,489	5,331
Accumulated net unrealized investment gain (loss) [Member]
Net Unrealized Gains Losses [Line Items]
Available-for-sale Securities, Accumulated Gross Unrealized Gain (Loss), before Tax	349,568	263,188
Net Unrealized gains losses on investments in Accumulated other comprehensive Income	$ 157,275	$ 120,673