ACCRUED EXPENSES AND OTHER LIABILITIES - Summary (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accrued Expenses
Salaries and wages	$ 158,122	$ 126,119
Deferred compensation	5,117	6,436
Pension benefits	3,776	3,863
Other postretirement benefits	1,381	1,478
Other employee benefits	20,599	21,577
Insurance obligations	169,936	163,763
Operating taxes (2)	164,293	116,003
Income taxes	4,588	2,873
Interest	38,887	46,032
Deposits, mainly from customers	79,840	82,573
Operating lease liabilities	78,785	72,285
Deferred revenue	183,474	165,205
Restructuring liabilities	7,683	6,765
Other	72,697	61,105
Total	989,178	876,077
Non-Current Liabilities
Salaries and wages	0	0
Deferred compensation	77,823	65,006
Pension benefits	265,178	413,829
Other postretirement benefits	20,245	20,187
Other employee benefits	0	0
Insurance obligations	292,298	285,838
Operating taxes (2)	41,687	0
Income taxes	15,598	17,484
Interest	0	0
Deposits, mainly from customers	3,014	3,065
Operating lease liabilities	186,429	151,361
Deferred revenue	446,265	438,482
Restructuring liabilities	0	0
Other	55,324	46,751
Total	1,403,861	1,442,003
Total
Salaries and wages	158,122	126,119
Deferred compensation	82,940	71,442
Pension benefits	268,954	417,692
Other postretirement benefits	21,626	21,665
Other employee benefits	20,599	21,577
Insurance obligations	462,234	449,601
Operating taxes (2)	205,980	116,003
Income taxes	20,186	20,357
Interest	38,887	46,032
Deposits, mainly from customers	82,854	85,638
Operating lease liabilities	265,214	223,646
Deferred revenue	629,739	603,687	$ 582,078
Restructuring liabilities	7,683	6,765
Other	128,021	107,856
Total	$ 2,393,039	$ 2,318,080