REINSURANCE - Receivables (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Reinsurance
Reinsurance receivables	$ 5,075,698	$ 5,323,846
Reinsurer Concentration Risk | Security Life of Denver Insurance Company | A
Reinsurance
Reinsurance receivables	740,800	762,200
Reinsurer Concentration Risk | Swiss Re Life & Health America, Inc. | A plus
Reinsurance
Reinsurance receivables	614,800	682,600
Reinsurer Concentration Risk | Lincoln National Life Insurance Co. | A plus
Reinsurance
Reinsurance receivables	489,100	530,900
Reinsurer Concentration Risk | Transamerica Life Insurance Co. | A plus
Reinsurance
Reinsurance receivables	335,600	367,800
Reinsurer Concentration Risk | SCOR Global Life | A
Reinsurance
Reinsurance receivables	331,800	354,800
Reinsurer Concentration Risk | RGA Reinsurance Company | A plus
Reinsurance
Reinsurance receivables	278,300	269,000
Reinsurer Concentration Risk | American United Life Insurance Company | A plus
Reinsurance
Reinsurance receivables	266,700	285,600
Reinsurer Concentration Risk | Scottish Re (U.S.) Inc.
Reinsurance
Reinsurance receivables	249,500	232,800
Reinsurer Concentration Risk | Centre Reinsurance (Bermuda) Ltd
Reinsurance
Reinsurance receivables	212,200	243,600
Reinsurer Concentration Risk | Employers Reassurance Corporation | A plus
Reinsurance
Reinsurance receivables	$ 193,900	$ 201,700