Supplemental Schedule of Reinsurance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums, Life Insurance in Force	$ 1,363,000	$ 1,462,000	$ 1,576,000
Ceded Premiums, Life Insurance in Force	186,172,000	205,529,000	214,727,000
Assumed Premiums, Life Insurance in Force	3,329,181,000	3,297,275,000	3,062,525,000
Premiums, Net, Life Insurance in Force	$ 3,144,372,000	$ 3,093,208,000	$ 2,849,374,000
Life Insurance in Force Premiums, Percentage Assumed to Net	105.90%	106.60%	107.50%
Direct Premiums Earned	$ 62,526	$ 61,571	$ 57,562
Reinsurance Premiums for Insurance Companies, by Product Segment, Amount Ceded to Other Companies	860,034	862,903	858,278
Assumed Premiums Earned	11,341,284	10,642,462	10,049,587
Reinsurance Premiums for Insurance Companies, by Product Segment, Net Amount	$ 10,543,776	$ 9,841,130	$ 9,248,871
Reinsurance Premiums for Insurance Companies, by Product Segment, Percentage of Amount Assumed to Net	107.60%	108.10%	108.70%
US Traditional Segment Reporting Information [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Earned	$ 31,600	$ 30,500	$ 31,600
Reinsurance Premiums for Insurance Companies, by Product Segment, Amount Ceded to Other Companies	593,700	610,400	616,000
Assumed Premiums Earned	6,095,400	5,936,200	5,834,000
Reinsurance Premiums for Insurance Companies, by Product Segment, Net Amount	$ 5,533,300	$ 5,356,300	$ 5,249,600
Reinsurance Premiums for Insurance Companies, by Product Segment, Percentage of Amount Assumed to Net	110.20%	110.80%	111.10%
US Non-Traditional Segment Reporting Information [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Earned	$ 4,700	$ 4,300	$ 1,600
Reinsurance Premiums for Insurance Companies, by Product Segment, Amount Ceded to Other Companies	0	0	40,200
Assumed Premiums Earned	22,500	19,400	63,000
Reinsurance Premiums for Insurance Companies, by Product Segment, Net Amount	$ 27,200	$ 23,700	$ 24,400
Reinsurance Premiums for Insurance Companies, by Product Segment, Percentage of Amount Assumed to Net	82.70%	81.90%	258.20%
Canada Traditional Segment Reporting Information [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Earned	$ 0	$ 0	$ 0
Reinsurance Premiums for Insurance Companies, by Product Segment, Amount Ceded to Other Companies	46,900	38,100	36,500
Assumed Premiums Earned	1,070,900	940,100	965,100
Reinsurance Premiums for Insurance Companies, by Product Segment, Net Amount	$ 1,024,000	$ 902,000	$ 928,600
Reinsurance Premiums for Insurance Companies, by Product Segment, Percentage of Amount Assumed to Net	104.60%	104.20%	103.90%
Canada Non-Traditional Segment Reporting Information [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Earned	$ 0	$ 0	$ 0
Reinsurance Premiums for Insurance Companies, by Product Segment, Amount Ceded to Other Companies	0	0	0
Assumed Premiums Earned	43,400	38,200	38,700
Reinsurance Premiums for Insurance Companies, by Product Segment, Net Amount	$ 43,400	$ 38,200	$ 38,700
Reinsurance Premiums for Insurance Companies, by Product Segment, Percentage of Amount Assumed to Net	100.00%	100.00%	100.00%
EMEA Traditional Segment Reporting Information [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Earned	$ 26,000	$ 26,600	$ 24,100
Reinsurance Premiums for Insurance Companies, by Product Segment, Amount Ceded to Other Companies	25,900	34,900	30,900
Assumed Premiums Earned	1,423,100	1,310,000	1,146,900
Reinsurance Premiums for Insurance Companies, by Product Segment, Net Amount	$ 1,423,200	$ 1,301,700	$ 1,140,100
Reinsurance Premiums for Insurance Companies, by Product Segment, Percentage of Amount Assumed to Net	100.00%	100.60%	100.60%
EMEA Non-Traditional Segment Reporting Information [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Earned	$ 200	$ 200	$ 300
Reinsurance Premiums for Insurance Companies, by Product Segment, Amount Ceded to Other Companies	143,700	125,000	84,400
Assumed Premiums Earned	338,800	288,500	264,400
Reinsurance Premiums for Insurance Companies, by Product Segment, Net Amount	$ 195,300	$ 163,700	$ 180,300
Reinsurance Premiums for Insurance Companies, by Product Segment, Percentage of Amount Assumed to Net	173.50%	176.20%	146.60%
Asia Pacific Traditional Segment Reporting Information [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Earned	$ 0	$ 0	$ 0
Reinsurance Premiums for Insurance Companies, by Product Segment, Amount Ceded to Other Companies	49,800	54,500	50,300
Assumed Premiums Earned	2,346,200	2,107,500	1,731,800
Reinsurance Premiums for Insurance Companies, by Product Segment, Net Amount	$ 2,296,400	$ 2,053,000	$ 1,681,500
Reinsurance Premiums for Insurance Companies, by Product Segment, Percentage of Amount Assumed to Net	102.20%	102.70%	103.00%
Asia Pacific Non-Traditional Segment Reporting Information [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Earned	$ 0	$ 0	$ 0
Reinsurance Premiums for Insurance Companies, by Product Segment, Amount Ceded to Other Companies	0	0	0
Assumed Premiums Earned	900	2,400	5,400
Reinsurance Premiums for Insurance Companies, by Product Segment, Net Amount	$ 900	$ 2,400	$ 5,400
Reinsurance Premiums for Insurance Companies, by Product Segment, Percentage of Amount Assumed to Net	100.00%	100.00%	100.00%
Corporate And Other Segment Reporting Information [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Earned	$ 0	$ 0	$ 0
Reinsurance Premiums for Insurance Companies, by Product Segment, Amount Ceded to Other Companies	0	0	0
Assumed Premiums Earned	100	100	300
Reinsurance Premiums for Insurance Companies, by Product Segment, Net Amount	$ 100	$ 100	$ 300
Reinsurance Premiums for Insurance Companies, by Product Segment, Percentage of Amount Assumed to Net	100.00%	100.00%	100.00%