ACQUISITIONS (Fair Values of Net Assets Acquired and Liabilities Assumed) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Nov. 03, 2021	Jul. 23, 2021	Apr. 02, 2021	Dec. 31, 2020	Dec. 31, 2019	Apr. 30, 2019
Business Acquisition [Line Items]
Goodwill	$ 530,723				$ 211,956	$ 195,043
test IO
Business Acquisition [Line Items]
Cash and cash equivalents							$ 663
Trade receivables and contract assets							621
Prepaid and other current assets							150
Goodwill							11,926
Intangible assets							6,219
Property and equipment and other noncurrent assets							305
Total assets acquired							19,884
Accounts payable, accrued expenses and other current liabilities							993
Short-term debt							0
Long-term debt							0
Operating lease liability, noncurrent							0
Other noncurrent liabilities							1,568
Total liabilities assumed							2,561
Noncontrolling interest in consolidated subsidiaries							0
Net assets acquired							$ 17,323
PolSource
Business Acquisition [Line Items]
Cash and cash equivalents				$ 2,565
Trade receivables and contract assets				12,734
Prepaid and other current assets				814
Goodwill				125,339
Intangible assets				15,790
Property and equipment and other noncurrent assets				461
Total assets acquired				157,703
Accounts payable, accrued expenses and other current liabilities				5,337
Short-term debt				0
Long-term debt				0
Operating lease liability, noncurrent				157
Other noncurrent liabilities				4,037
Total liabilities assumed				9,531
Noncontrolling interest in consolidated subsidiaries				0
Net assets acquired				$ 148,172
CORE
Business Acquisition [Line Items]
Cash and cash equivalents			$ 11,283
Trade receivables and contract assets			10,266
Prepaid and other current assets			5,562
Goodwill			23,234
Intangible assets			8,368
Property and equipment and other noncurrent assets			4,585
Total assets acquired			63,298
Accounts payable, accrued expenses and other current liabilities			8,508
Short-term debt			0
Long-term debt			0
Operating lease liability, noncurrent			2,056
Other noncurrent liabilities			2,525
Total liabilities assumed			13,089
Noncontrolling interest in consolidated subsidiaries			0
Net assets acquired			$ 50,209
Emakina
Business Acquisition [Line Items]
Cash and cash equivalents		$ 5,142
Trade receivables and contract assets		34,389
Prepaid and other current assets		3,109
Goodwill		136,614
Intangible assets		30,488
Property and equipment and other noncurrent assets		17,059
Total assets acquired		226,801
Accounts payable, accrued expenses and other current liabilities		36,042
Short-term debt	16,000	13,657
Long-term debt	$ 5,200	8,874
Operating lease liability, noncurrent		5,411
Other noncurrent liabilities		8,337
Total liabilities assumed		72,321
Noncontrolling interest in consolidated subsidiaries		10,469
Net assets acquired		$ 144,011