CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Fixed maturities at fair value, amortized cost	$ 54,466,305	$ 41,153,551
Fixed maturities at amortized cost, fair value	2,547,210	2,776,327
Equity securities, cost	627,087	740,813
Mortgage loans, related to securitizations	134	226,409
Investment real estate, accumulated depreciation	251	132
Other intangibles, accumulated depreciation	197,583	140,368
Property and equipment, accumulated depreciation	$ 33,199	$ 22,926
Common Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common Stock, shares authorized (in shares)	5,000	5,000
Common Stock, shares issued (in shares)	1,000	1,000
Net unrealized gains (losses) on investments, income tax	$ (368,830)	$ 7,416
Net unrealized (losses) relating to other-than-temporary impaired investments for which a portion has been recognized in earnings, income tax	(6,054)	(538)
Accumulated loss - derivatives, income tax	(2)	198
Postretirement benefits liability adjustment, income tax	$ (4,112)	$ (3,469)