CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income (loss)	$ 25,768,000	$ (51,765,000)
Adjustments to reconcile net income (loss) to cash provided by (used in) operating activities:
Stock-based compensation	16,870,000	15,443,000
Depreciation	18,000,000	16,853,000
Amortization of intangibles	14,916,000	17,215,000
Amortization of deferred finance charges	2,018,000	8,736,000
Goodwill, Impairment Loss	0	29,631,000
Adjustment to deferred acquisition consideration	13,354,000	17,363,000
Deferred income tax	8,125,000	(553,000)
(Gain) loss on sale of assets	1,245,000	377,000
(Earnings) losses of non-consolidated affiliates	(1,924,000)	(9,000)
Other non-current assets and liabilities	(4,388,000)	1,853,000
Foreign exchange	(15,113,000)	(12,806,000)
Changes in working capital:
Accounts receivable	(54,723,000)	(47,767,000)
Expenditures billable to clients	(9,294,000)	5,551,000
Prepaid expenses and other current assets	6,400,000	(16,851,000)
Accounts payable, accruals and other liabilities	(31,149,000)	(77,355,000)
Advance billings	32,015,000	25,824,000
Net cash provided by (used in) operating activities	22,120,000	(41,387,000)
Cash flows used in investing activities:
Capital expenditures	(28,305,000)	(19,723,000)
Deposits	(1,461,000)	0
Acquisitions, net of cash acquired	0	2,531,000
Distributions from non-consolidated affiliates	(1,530,000)	(2,571,000)
Net Cash Provided by (Used in) Investing Activities	(19,503,000)	(14,663,000)
Cash flows provided by financing activities:
Acquisition related payments	(89,126,000)	(129,616,000)
Repayment of long-term debt	(310,000)	(381,000)
Purchase of shares	(1,239,000)	(2,798,000)
Premium paid on redemption of notes	0	(26,873,000)
Deferred financing costs	0	(21,569,000)
Distributions to noncontrolling interests	(5,272,000)	(6,549,000)
Payment of dividends	(284,000)	(32,580,000)
Net Cash Provided by (Used in) Financing Activities	(11,683,000)	15,131,000
Effect of exchange rate changes on cash and cash equivalents	6,000	1,196,000
Decrease in cash and cash equivalents	(9,060,000)	(39,723,000)
Cash and cash equivalents at beginning of period	27,921,000	61,458,000
Cash and cash equivalents at end of period	18,861,000	21,735,000
Supplemental disclosures:
Cash income taxes paid	6,909,000	2,798,000
Cash interest paid	32,324,000	27,979,000
Change in cash held in trusts	(159,000)	147,000
Non-cash transactions:
Capital leases	621,000	0
Dividends payable	453,000	1,077,000
Deferred acquisition consideration settled through issuance of shares	27,852,000
Proceeds from Sale of Other Assets, Investing Activities	11,120,000	215,000
Payments of Distributions to Affiliates	673,000	4,885,000
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable	0	34,219,000
Leasehold improvements financed by landlord	0	7,250,000
Six Point Seven Five Percentage Notes [Member]
Adjustments to reconcile net income (loss) to cash provided by (used in) operating activities:
Loss on redemption of notes	0	26,873,000
Cash flows provided by financing activities:
Repayment of 6.75% Notes	0	(735,000,000)
Six Point Five Zero Percentage Notes [Domain]
Cash flows provided by financing activities:
Proceeds from issuance of 6.50% Notes	0	900,000,000
Wells Fargo Capital Finance, LLC | Revolving Credit Facility [Member]
Cash flows provided by financing activities:
Repayments of revolving credit agreement	(1,093,508,000)	(1,255,608,000)
Proceeds from revolving credit agreement	1,087,688,000	1,326,105,000
Common Stock [Member]
Non-cash transactions:
Deferred acquisition consideration settled through issuance of shares	28,727,000
Series 4 Convertible Preferred Stock [Domain]
Cash flows provided by financing activities:
Proceeds from issuance of convertible preference shares	95,000,000	0
Convertible Preferred Stock [Member]
Cash flows provided by financing activities:
Convertible preference shares issuance costs	$ (4,632,000)	0
Common Class A [Member] | Common Stock [Member]
Non-cash transactions:
Deferred acquisition consideration settled through issuance of shares		$ 10,458,000