REVENUE FROM CONTRACTS WITH CUSTOMERS - Impact on Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets:
Receivables, net of allowance for doubtful accounts	$ 2,162,438	$ 2,012,212	$ 2,113,930
Contract assets	159,635	147,764	0
Prepaid expenses and other	52,386		63,116
Prepaid expenses and other		67,137
Liabilities:
Accounts payable	971,023	943,812	1,000,305
Accrued expenses - compensation	153,626	107,280	105,316
Accrued expenses - transportation expense	119,820	94,811	0
Accrued expenses - other accrued liabilities	63,410	55,477	58,229
Deferred tax liabilities	35,757	48,653	45,355
Equity:
Retained earnings	3,845,593	3,446,332	3,437,093
Calculated under Revenue Guidance in Effect before Topic 606
Assets:
Receivables, net of allowance for doubtful accounts	2,223,632		2,113,930
Contract assets	0		0
Prepaid expenses and other	50,683		63,116
Liabilities:
Accounts payable	1,009,758		1,000,305
Accrued expenses - compensation	151,280		105,316
Accrued expenses - transportation expense	0		0
Accrued expenses - other accrued liabilities	66,116		58,229
Deferred tax liabilities	30,599		45,355
Equity:
Retained earnings	3,831,332		$ 3,437,093
Difference between Revenue Guidance in Effect before and after Topic 606 | ASU No. 2014-09
Assets:
Receivables, net of allowance for doubtful accounts	(61,194)	(101,718)
Contract assets	159,635	147,764
Prepaid expenses and other	1,703	4,021
Liabilities:
Accounts payable	(38,735)	(56,493)
Accrued expenses - compensation	2,346	1,964
Accrued expenses - transportation expense	119,820	94,811
Accrued expenses - other accrued liabilities	(2,706)	(2,752)
Deferred tax liabilities	5,158	3,298
Equity:
Retained earnings	$ 14,261	$ 9,239