Revision to Prior Year Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
ASSETS
Reinsurance recoverables	$ 31,935,722		$ 31,935,722		$ 32,521,264
TOTAL ASSETS	169,832,225		169,832,225		172,425,340
LIABILITIES
Future policy benefits	17,199,539		17,199,539		18,561,550
Income taxes	11,546		11,546		36,323
Other liabilities	953,596		953,596		1,038,972
TOTAL LIABILITIES	167,122,244		167,122,244		169,590,092
EQUITY
Retained earnings	1,551,327		1,551,327		1,526,310
TOTAL EQUITY	2,709,981		2,709,981		2,835,248
TOTAL LIABILITIES AND EQUITY	169,832,225		169,832,225		172,425,340
REVENUES
Policy charges and fee income	169,004	$ (116,167)	298,159	$ 11,835
TOTAL REVENUES	248,288	287,079	437,000	498,038
BENEFITS AND EXPENSES
Policyholders’ benefits	40,441	(181,098)	92,177	(113,179)
TOTAL BENEFITS AND EXPENSES	224,981	(44,363)	404,450	141,407
INCOME (LOSS) FROM OPERATIONS BEFORE INCOME TAXES AND EQUITY IN EARNINGS OF OPERATING JOINT VENTURE	23,307	331,442	32,550	356,631
Income tax expense (benefit)	(13,012)	(9,610)	(15,711)	(30,438)
INCOME (LOSS) FROM OPERATIONS BEFORE EQUITY IN EARNINGS OF OPERATING JOINT VENTURE	36,319	341,052	48,261	387,069
Net income (loss)	36,226	341,052	47,530	387,069
COMPREHENSIVE INCOME (LOSS)	(33,081)	407,508	(137,051)	471,222
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	36,226	341,052	47,530	387,069
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	36,226	341,052	47,530	387,069
Policy charges and fee income			(75,175)	(73,450)
Future policy benefits			870,715	999,298
Reinsurance recoverables			(799,012)	(1,116,831)
Income taxes			22,585	13,357
Other, net			(127,216)	87,749
Cash flows from (used in) operating activities			(15,457)	19,356
As previously reported
ASSETS
Reinsurance recoverables					32,555,500
TOTAL ASSETS					172,459,576
LIABILITIES
Future policy benefits					18,593,130
Income taxes					32,440
Other liabilities					1,060,123
TOTAL LIABILITIES					169,638,940
EQUITY
Retained earnings					1,511,698
TOTAL EQUITY					2,820,636
TOTAL LIABILITIES AND EQUITY					172,459,576
REVENUES
Policy charges and fee income		(132,525)		(4,523)
TOTAL REVENUES		270,721		481,680
BENEFITS AND EXPENSES
Policyholders’ benefits		(204,017)		(132,530)
TOTAL BENEFITS AND EXPENSES		(67,282)		122,056
INCOME (LOSS) FROM OPERATIONS BEFORE INCOME TAXES AND EQUITY IN EARNINGS OF OPERATING JOINT VENTURE		338,003		359,624
Income tax expense (benefit)		(11,161)		(29,612)
INCOME (LOSS) FROM OPERATIONS BEFORE EQUITY IN EARNINGS OF OPERATING JOINT VENTURE		349,164		389,236
Net income (loss)		349,164		389,236
COMPREHENSIVE INCOME (LOSS)		415,620		473,389
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		349,164		389,236
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)		349,164		389,236
Future policy benefits				1,006,435
Reinsurance recoverables				(1,143,319)
Income taxes				14,183
Other, net				104,107
Cash flows from (used in) operating activities				19,356
Revision
ASSETS
Reinsurance recoverables					(34,236)
TOTAL ASSETS					(34,236)
LIABILITIES
Future policy benefits					(31,580)
Income taxes					3,883
Other liabilities					(21,151)
TOTAL LIABILITIES					(48,848)
EQUITY
Retained earnings					14,612
TOTAL EQUITY					14,612
TOTAL LIABILITIES AND EQUITY					$ (34,236)
REVENUES
Policy charges and fee income		16,358		16,358
TOTAL REVENUES		16,358		16,358
BENEFITS AND EXPENSES
Policyholders’ benefits		22,919		19,351
TOTAL BENEFITS AND EXPENSES		22,919		19,351
INCOME (LOSS) FROM OPERATIONS BEFORE INCOME TAXES AND EQUITY IN EARNINGS OF OPERATING JOINT VENTURE		(6,561)		(2,993)
Income tax expense (benefit)		1,551		(826)
INCOME (LOSS) FROM OPERATIONS BEFORE EQUITY IN EARNINGS OF OPERATING JOINT VENTURE		(8,112)		(2,167)
Net income (loss)		(8,112)		(2,167)
COMPREHENSIVE INCOME (LOSS)		(8,112)		(2,167)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		(8,112)		(2,167)
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)		(8,112)		(2,167)
Future policy benefits				(7,137)
Reinsurance recoverables				26,488
Income taxes				(826)
Other, net				(16,358)
Cash flows from (used in) operating activities				0
Retained Earnings
BENEFITS AND EXPENSES
Net income (loss)			47,530	387,069
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			1,526,310	1,448,517
Net income (loss)			47,530	387,069
Ending Balance	1,551,327	1,835,586	1,551,327	1,835,586
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)			47,530	387,069
Retained Earnings | As previously reported
BENEFITS AND EXPENSES
Net income (loss)				389,236
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			1,511,698	1,437,266
Net income (loss)				389,236
Ending Balance		1,826,502		1,826,502
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)				389,236
Retained Earnings | Revision
BENEFITS AND EXPENSES
Net income (loss)				(2,167)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			14,612	11,251
Net income (loss)				(2,167)
Ending Balance		9,084		9,084
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)				(2,167)
Total Equity
BENEFITS AND EXPENSES
Net income (loss)			47,530	387,069
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			2,835,248	2,508,054
Net income (loss)			47,530	387,069
Total comprehensive income (loss)			(137,051)	471,222
Ending Balance	$ 2,709,981	2,985,151	2,709,981	2,985,151
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)			47,530	387,069
Total Equity | As previously reported
BENEFITS AND EXPENSES
Net income (loss)				389,236
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			2,820,636	2,496,803
Net income (loss)				389,236
Total comprehensive income (loss)				473,389
Ending Balance		2,976,067		2,976,067
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)				389,236
Total Equity | Revision
BENEFITS AND EXPENSES
Net income (loss)				(2,167)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			$ 14,612	11,251
Net income (loss)				(2,167)
Total comprehensive income (loss)				(2,167)
Ending Balance		$ 9,084		9,084
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)				$ (2,167)