REVENUE (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue
Revenue	$ 1,287,624	$ 1,416,078	$ 2,544,432	$ 2,758,562
Manufacturer's rebates earned on total gross profit (in percent)	9.60%	22.30%	10.60%	14.80%
Inter-segment eliminations
Revenue
Revenue	$ (18,458)	$ (6,415)	$ (27,932)	$ (8,378)
Specialty
Revenue
Revenue	1,215,769	1,233,746	2,384,134	2,386,725
PBM
Revenue
Revenue	90,313	188,747	188,230	380,215
Oncology | Specialty
Revenue
Revenue	718,081	706,291	1,404,715	1,393,188
Specialty infusion | Specialty
Revenue
Revenue	192,156	181,250	370,604	346,967
Immunology | Specialty
Revenue
Revenue	140,836	142,952	276,528	278,551
Other | Specialty
Revenue
Revenue	164,696	203,253	332,287	368,019
Retail networks | PBM
Revenue
Revenue	57,784	146,127	125,196	291,288
Specialty pharmacy | PBM
Revenue
Revenue	18,070	23,001	34,167	45,314
Mail order | PBM
Revenue
Revenue	11,817	17,018	22,782	34,010
Other | PBM
Revenue
Revenue	$ 2,642	$ 2,601	$ 6,085	$ 9,603