REINSURANCE - Receivables (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Reinsurance
Reinsurance receivables	$ 4,764,743	$ 5,075,698
Reinsurer Concentration Risk | Security Life of Denver Insurance Company | A
Reinsurance
Reinsurance receivables	722,200	740,800
Reinsurer Concentration Risk | Swiss Re Life & Health America, Inc. | A plus
Reinsurance
Reinsurance receivables	603,800	614,800
Reinsurer Concentration Risk | Lincoln National Life Insurance Co. | A plus
Reinsurance
Reinsurance receivables	461,100	489,100
Reinsurer Concentration Risk | SCOR Global Life(1) | A plus
Reinsurance
Reinsurance receivables	317,200	331,800
Reinsurer Concentration Risk | Transamerica Life Insurance Co. | A plus
Reinsurance
Reinsurance receivables	301,000	335,600
Reinsurer Concentration Risk | RGA Reinsurance Company | A plus
Reinsurance
Reinsurance receivables	260,500	278,300
Reinsurer Concentration Risk | American United Life Insurance Company | A plus
Reinsurance
Reinsurance receivables	242,800	266,700
Reinsurer Concentration Risk | Centre Reinsurance (Bermuda) Ltd
Reinsurance
Reinsurance receivables	197,400	212,200
Reinsurer Concentration Risk | The Canada Life Assurance Company | A plus
Reinsurance
Reinsurance receivables	188,200	186,100
Reinsurer Concentration Risk | Employers Reassurance Corporation | B plus
Reinsurance
Reinsurance receivables	$ 178,400	$ 193,900