REVENUES (Disaggregation of Revenues) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Disaggregation of Revenue [Line Items]
Revenues	$ 1,170,206	$ 1,194,861	$ 2,381,147	$ 2,366,475
Revenues from performance obligations satisfied in previous period	3,500		5,600
Increase (decrease) in contract with customer, liability		12,500		6,600
Transferred over time
Disaggregation of Revenue [Line Items]
Revenues	1,166,309	1,193,398	2,373,564	2,362,246
Transferred at a point of time
Disaggregation of Revenue [Line Items]
Revenues	3,897	1,463	7,583	4,229
Time-and-material
Disaggregation of Revenue [Line Items]
Revenues	1,028,020	1,059,571	2,102,999	2,082,724
Fixed-price
Disaggregation of Revenue [Line Items]
Revenues	135,353	131,180	265,858	274,743
Licensing and other revenues
Disaggregation of Revenue [Line Items]
Revenues	6,833	4,110	12,290	9,008
Travel & Consumer
Disaggregation of Revenue [Line Items]
Revenues	273,459	276,318	551,819	541,637
Financial Services
Disaggregation of Revenue [Line Items]
Revenues	258,968	250,983	529,633	511,046
Business Information & Media
Disaggregation of Revenue [Line Items]
Revenues	189,684	197,870	392,064	392,173
Software & Hi-Tech
Disaggregation of Revenue [Line Items]
Revenues	175,218	195,323	364,409	384,806
Life Sciences & Healthcare
Disaggregation of Revenue [Line Items]
Revenues	114,441	128,492	225,699	252,295
Emerging Verticals
Disaggregation of Revenue [Line Items]
Revenues	158,436	145,875	317,523	284,518
Americas
Disaggregation of Revenue [Line Items]
Revenues	679,087	721,612	1,388,889	1,408,405
EMEA
Disaggregation of Revenue [Line Items]
Revenues	459,085	422,986	923,022	844,936
APAC
Disaggregation of Revenue [Line Items]
Revenues	24,219	30,176	51,029	59,758
CEE
Disaggregation of Revenue [Line Items]
Revenues	7,815	20,087	18,207	53,376
North America
Disaggregation of Revenue [Line Items]
Revenues	680,071	723,657	1,390,028	1,411,368
North America | Transferred over time
Disaggregation of Revenue [Line Items]
Revenues	676,637	722,311	1,383,671	1,407,420
North America | Transferred at a point of time
Disaggregation of Revenue [Line Items]
Revenues	3,434	1,346	6,357	3,948
North America | Time-and-material
Disaggregation of Revenue [Line Items]
Revenues	606,766	654,627	1,251,394	1,281,434
North America | Fixed-price
Disaggregation of Revenue [Line Items]
Revenues	67,273	65,992	128,504	122,757
North America | Licensing and other revenues
Disaggregation of Revenue [Line Items]
Revenues	6,032	3,038	10,130	7,177
North America | Travel & Consumer
Disaggregation of Revenue [Line Items]
Revenues	120,038	130,932	243,697	253,179
North America | Financial Services
Disaggregation of Revenue [Line Items]
Revenues	135,178	126,879	279,028	247,214
North America | Business Information & Media
Disaggregation of Revenue [Line Items]
Revenues	106,357	114,026	222,515	224,972
North America | Software & Hi-Tech
Disaggregation of Revenue [Line Items]
Revenues	135,755	161,034	285,553	317,316
North America | Life Sciences & Healthcare
Disaggregation of Revenue [Line Items]
Revenues	99,966	115,899	196,563	227,270
North America | Emerging Verticals
Disaggregation of Revenue [Line Items]
Revenues	82,777	74,887	162,672	141,417
North America | Americas
Disaggregation of Revenue [Line Items]
Revenues	653,601	697,961	1,337,154	1,357,737
North America | EMEA
Disaggregation of Revenue [Line Items]
Revenues	25,629	23,190	51,001	48,288
North America | APAC
Disaggregation of Revenue [Line Items]
Revenues	649	793	1,375	1,576
North America | CEE
Disaggregation of Revenue [Line Items]
Revenues	192	1,713	498	3,767
Europe
Disaggregation of Revenue [Line Items]
Revenues	483,442	451,944	976,589	903,914
Europe | Transferred over time
Disaggregation of Revenue [Line Items]
Revenues	482,999	451,847	975,396	903,695
Europe | Transferred at a point of time
Disaggregation of Revenue [Line Items]
Revenues	443	97	1,193	219
Europe | Time-and-material
Disaggregation of Revenue [Line Items]
Revenues	416,194	390,296	841,792	767,951
Europe | Fixed-price
Disaggregation of Revenue [Line Items]
Revenues	66,468	60,607	132,671	134,215
Europe | Licensing and other revenues
Disaggregation of Revenue [Line Items]
Revenues	780	1,041	2,126	1,748
Europe | Travel & Consumer
Disaggregation of Revenue [Line Items]
Revenues	151,639	140,081	304,694	276,869
Europe | Financial Services
Disaggregation of Revenue [Line Items]
Revenues	120,361	112,766	243,969	230,096
Europe | Business Information & Media
Disaggregation of Revenue [Line Items]
Revenues	83,260	83,681	169,368	166,582
Europe | Software & Hi-Tech
Disaggregation of Revenue [Line Items]
Revenues	38,910	33,847	77,592	66,301
Europe | Life Sciences & Healthcare
Disaggregation of Revenue [Line Items]
Revenues	14,454	12,527	28,980	24,809
Europe | Emerging Verticals
Disaggregation of Revenue [Line Items]
Revenues	74,818	69,042	151,986	139,257
Europe | Americas
Disaggregation of Revenue [Line Items]
Revenues	25,150	22,816	51,104	48,776
Europe | EMEA
Disaggregation of Revenue [Line Items]
Revenues	433,456	399,796	872,021	796,549
Europe | APAC
Disaggregation of Revenue [Line Items]
Revenues	23,570	29,383	49,654	58,182
Europe | CEE
Disaggregation of Revenue [Line Items]
Revenues	1,266	(51)	3,810	407
Russia
Disaggregation of Revenue [Line Items]
Revenues	6,693	19,260	14,530	51,193
Russia | Transferred over time
Disaggregation of Revenue [Line Items]
Revenues	6,673	19,240	14,497	51,131
Russia | Transferred at a point of time
Disaggregation of Revenue [Line Items]
Revenues	20	20	33	62
Russia | Time-and-material
Disaggregation of Revenue [Line Items]
Revenues	5,060	14,648	9,813	33,339
Russia | Fixed-price
Disaggregation of Revenue [Line Items]
Revenues	1,612	4,581	4,683	17,771
Russia | Licensing and other revenues
Disaggregation of Revenue [Line Items]
Revenues	21	31	34	83
Russia | Travel & Consumer
Disaggregation of Revenue [Line Items]
Revenues	1,782	5,305	3,428	11,589
Russia | Financial Services
Disaggregation of Revenue [Line Items]
Revenues	3,429	11,338	6,636	33,736
Russia | Business Information & Media
Disaggregation of Revenue [Line Items]
Revenues	67	163	181	619
Russia | Software & Hi-Tech
Disaggregation of Revenue [Line Items]
Revenues	553	442	1,264	1,189
Russia | Life Sciences & Healthcare
Disaggregation of Revenue [Line Items]
Revenues	21	66	156	216
Russia | Emerging Verticals
Disaggregation of Revenue [Line Items]
Revenues	841	1,946	2,865	3,844
Russia | Americas
Disaggregation of Revenue [Line Items]
Revenues	336	835	631	1,892
Russia | EMEA
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	99
Russia | APAC
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Russia | CEE
Disaggregation of Revenue [Line Items]
Revenues	$ 6,357	$ 18,425	$ 13,899	$ 49,202