Revision to Prior Year Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
ASSETS
Reinsurance recoverables	$ 31,430,148		$ 31,430,148		$ 32,521,264
TOTAL ASSETS	172,561,326		172,561,326		172,425,340
LIABILITIES
Future policy benefits	16,498,119		16,498,119		18,561,550
Income taxes payable	0		0		36,323
Other liabilities	1,084,739		1,084,739		1,038,972
TOTAL LIABILITIES	169,862,932		169,862,932		169,590,092
EQUITY
Retained earnings	1,570,052		1,570,052		1,526,310
TOTAL EQUITY	2,698,394		2,698,394		2,835,248
TOTAL LIABILITIES AND EQUITY	172,561,326		172,561,326		172,425,340
REVENUES
Policy charges and fee income	106,926	$ 129,105	405,085	$ 140,940
TOTAL REVENUES	183,330	(21,860)	620,330	476,178
BENEFITS AND EXPENSES
Policyholders’ benefits	9,823	54,944	102,000	(58,235)
TOTAL BENEFITS AND EXPENSES	166,760	193,996	571,210	335,403
INCOME (LOSS) FROM OPERATIONS BEFORE INCOME TAXES AND EQUITY IN EARNINGS OF OPERATING JOINT VENTURE	16,570	(215,856)	49,120	140,775
Income tax expense (benefit)	(2,760)	(38,660)	(18,471)	(69,098)
INCOME (LOSS) FROM OPERATIONS BEFORE EQUITY IN EARNINGS OF OPERATING JOINT VENTURE	19,330	(177,196)	67,591	209,873
Net income (loss)	18,725	(177,196)	66,255	209,873
COMPREHENSIVE INCOME (LOSS)	(11,700)	(183,651)	(148,751)	287,571
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	18,725	(177,196)	66,255	209,873
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	18,725	(177,196)	66,255	209,873
Policy charges and fee income			(97,276)	(124,187)
Future policy benefits			1,392,199	1,455,418
Reinsurance recoverables			(1,304,316)	(1,564,329)
Income taxes			10,708	53,472
Other, net			(70,025)	90,529
Cash flows from (used in) operating activities			19,415	85,494
As previously reported
ASSETS
Reinsurance recoverables					32,555,500
TOTAL ASSETS					172,459,576
LIABILITIES
Future policy benefits					18,593,130
Income taxes payable					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		126,709		122,186
TOTAL REVENUES		(24,256)		457,424
BENEFITS AND EXPENSES
Policyholders’ benefits		54,637		(77,893)
TOTAL BENEFITS AND EXPENSES		193,689		315,745
INCOME (LOSS) FROM OPERATIONS BEFORE INCOME TAXES AND EQUITY IN EARNINGS OF OPERATING JOINT VENTURE		(217,945)		141,679
Income tax expense (benefit)		(39,449)		(69,061)
INCOME (LOSS) FROM OPERATIONS BEFORE EQUITY IN EARNINGS OF OPERATING JOINT VENTURE		(178,496)		210,740
Net income (loss)		(178,496)		210,740
COMPREHENSIVE INCOME (LOSS)		(184,951)		288,438
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		(178,496)		210,740
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)		(178,496)		210,740
Future policy benefits				1,466,123
Reinsurance recoverables				(1,594,691)
Income taxes				53,508
Other, net				109,283
Cash flows from (used in) operating activities				85,494
Revision
ASSETS
Reinsurance recoverables					(34,236)
TOTAL ASSETS					(34,236)
LIABILITIES
Future policy benefits					(31,580)
Income taxes payable					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		2,396		18,754
TOTAL REVENUES		2,396		18,754
BENEFITS AND EXPENSES
Policyholders’ benefits		307		19,658
TOTAL BENEFITS AND EXPENSES		307		19,658
INCOME (LOSS) FROM OPERATIONS BEFORE INCOME TAXES AND EQUITY IN EARNINGS OF OPERATING JOINT VENTURE		2,089		(904)
Income tax expense (benefit)		789		(37)
INCOME (LOSS) FROM OPERATIONS BEFORE EQUITY IN EARNINGS OF OPERATING JOINT VENTURE		1,300		(867)
Net income (loss)		1,300		(867)
COMPREHENSIVE INCOME (LOSS)		1,300		(867)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		1,300		(867)
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)		1,300		(867)
Future policy benefits				(10,705)
Reinsurance recoverables				30,362
Income taxes				(36)
Other, net				(18,754)
Cash flows from (used in) operating activities				0
Retained Earnings
BENEFITS AND EXPENSES
Net income (loss)			66,255	209,873
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			1,526,310	1,448,517
Net income (loss)			66,255	209,873
Ending Balance	1,570,052	1,658,390	1,570,052	1,658,390
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)			66,255	209,873
Retained Earnings | As previously reported
BENEFITS AND EXPENSES
Net income (loss)				210,740
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			1,511,698	1,437,266
Net income (loss)				210,740
Ending Balance		1,648,006		1,648,006
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)				210,740
Retained Earnings | Revision
BENEFITS AND EXPENSES
Net income (loss)				(867)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			14,612	11,251
Net income (loss)				(867)
Ending Balance		10,384		10,384
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)				(867)
Total Equity
BENEFITS AND EXPENSES
Net income (loss)			66,255	209,873
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			2,835,248	2,508,054
Net income (loss)			66,255	209,873
Total comprehensive income (loss)			(148,751)	287,571
Ending Balance	$ 2,698,394	2,950,000	2,698,394	2,950,000
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)			66,255	209,873
Total Equity | As previously reported
BENEFITS AND EXPENSES
Net income (loss)				210,740
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			2,820,636	2,496,803
Net income (loss)				210,740
Total comprehensive income (loss)				288,438
Ending Balance		2,939,616		2,939,616
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)				210,740
Total Equity | Revision
BENEFITS AND EXPENSES
Net income (loss)				(867)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			$ 14,612	11,251
Net income (loss)				(867)
Total comprehensive income (loss)				(867)
Ending Balance		$ 10,384		10,384
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)				$ (867)