BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Impact of Reclassifications on the Consolidated Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets
Accounts receivable, net of allowance of $1,557		$ 0
Unbilled revenues		0
Trade receivables and contract assets, net of allowance of $1,557	$ 497,716	402,337
Current liabilities
Accrued expenses and other current liabilities	82,476	50,253
Accrued compensation and benefits expenses	230,035	177,594
Due to employees		0
Deferred compensation due to employees		0
Taxes payable, current		0
Income taxes payable, current	$ 9,064	27,538
As Previously Reported
Current assets
Accounts receivable, net of allowance of $1,557		297,685
Unbilled revenues		104,652
Trade receivables and contract assets, net of allowance of $1,557		0
Current liabilities
Accrued expenses and other current liabilities		127,937
Accrued compensation and benefits expenses		0
Due to employees		49,683
Deferred compensation due to employees		9,920
Taxes payable, current		67,845
Income taxes payable, current		0
Change
Current assets
Accounts receivable, net of allowance of $1,557		(297,685)
Unbilled revenues		(104,652)
Trade receivables and contract assets, net of allowance of $1,557		402,337
Current liabilities
Accrued expenses and other current liabilities		(77,684)
Accrued compensation and benefits expenses		177,594
Due to employees		(49,683)
Deferred compensation due to employees		(9,920)
Taxes payable, current		(67,845)
Income taxes payable, current		$ 27,538