ACQUISITIONS (Fair Values of Net Assets Acquired and Liabilities Assumed) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Nov. 01, 2018	Mar. 15, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Unbilled revenues	$ 104,652			$ 86,422	$ 86,500
Goodwill	$ 166,832				$ 119,531	$ 109,289
Continuum
Business Acquisition [Line Items]
Cash and cash equivalents			$ 2,251
Accounts receivable			6,676
Unbilled revenues			2,463
Prepaid and other current assets			936
Goodwill			26,617
Intangible assets			14,450
Property and equipment and other noncurrent assets			8,902
Total assets acquired			62,295
Accounts payable, accrued expenses and other current liabilities			2,745
Due to employees			1,001
Long-term debt (Note 8)			3,220
Other noncurrent liabilities			490
Total liabilities assumed			7,456
Net assets acquired			$ 54,839
Think
Business Acquisition [Line Items]
Cash and cash equivalents		$ 2,344
Accounts receivable		2,259
Unbilled revenues		284
Prepaid and other current assets		609
Goodwill		22,482
Intangible assets		6,882
Property and equipment and other noncurrent assets		642
Total assets acquired		35,502
Accounts payable, accrued expenses and other current liabilities		2,205
Due to employees		13
Long-term debt (Note 8)		0
Other noncurrent liabilities		1,040
Total liabilities assumed		3,258
Net assets acquired		$ 32,244