ACQUISITIONS AND DIVESTITURES (NARRATIVE) (DETAILS) $ in Thousands, CAD in Millions				3 Months Ended								12 Months Ended
	Nov. 09, 2016 CAD	Aug. 08, 2014 USD ($)	Feb. 28, 2014 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Nov. 09, 2016 USD ($)
Business Acquisition [Line Items]
Contingent Consideration, at fair value					$ 1,808		$ 13,450			$ 24,744		$ 1,808	$ 13,450	$ 24,744
Loss on assets held-for-sale												5,300	0	0
Investments in non-marketable equity investments												$ 3,179	9,000	0
Customer Growth Services
Business Acquisition [Line Items]
Loss on assets held-for-sale						$ 2,600
Customer Strategy Services
Business Acquisition [Line Items]
Loss on assets held-for-sale						2,700
Atelka [Member]
Business Acquisition [Line Items]
Date of Acquisition	Nov. 09, 2016
Description of Acquired Entity	On November 9, 2016, the Company acquired all of the outstanding shares of Atelka Enterprise Inc. ("Atelka"), a Canadian customer contact center management and business process outsourcing services company that serves Canadian telecommunications, logistics, and entertainment clients. This acquisition is an addition to the Customer Management Services ("CMS") segment. Atelka employs approximately 2,800 in Quebec, Ontario, New Brunswick and Prince Edward Island.
Total purchase price															$ 48,787
Cost of Acquired Entity, Up Front Cash Consideration															47,500
Acquisition hold-back payment															$ 1,400
Discount rate												0.00%
Contingent Consideration, at fair value					558		0					$ 558	0
Atelka [Member] | CAD
Business Acquisition [Line Items]
Total purchase price | CAD	CAD 65.2
Atelka [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	12 years
rogenSi [Member]
Business Acquisition [Line Items]
Description of Acquired Entity		rogenSi Worldwide PTY, Ltd., a global leadership, change management, sales, performance training and consulting company
Total purchase price		$ 34,400
Cost of Acquired Entity, Up Front Cash Consideration		18,100
Future Value of Liabilities Incurred From Business Acquisitions		$ 15,300
Valuation Technique on Contingent Consideration		The fair value of the contingent consideration was measured by applying a probability weighted discounted cash flow model based on significant inputs not observable in the market (Level 3 inputs). Key assumptions include a discount rate of 4.6% and expected future value of payments of $15.3 million. The $15.3 million of expected future payments was calculated using a probability weighted EBITDA assessment with the highest probability associated with rogenSi achieving the targeted EBITDA for each earn-out year.
Acquisition hold-back payment		$ 1,800
Discount rate		4.60%
Contingent Consideration Arrangements, Basis for Amount		The total contingent consideration possible per the sale and purchase agreement ranged from zero to $17.6 million and the earn-out payments were payable in early 2015, 2016 and 2017, based on July 1, 2014 through December 31, 2014, and full year 2015 and 2016 performance, respectively.
Contingent Consideration, at fair value		$ 14,500			0		9,797			15,162		0	9,797	15,162
Increase (decrease) in contingent consideration payable						$ (4,300)	(300)	$ 800		500
Sofica [Member]
Business Acquisition [Line Items]
Percentage of Voting Interests Acquired			100.00%
Description of Acquired Entity			Sofica provides customer lifecycle management and other business process services across multiple channels in multiple sites in over 18 languages.
Total purchase price			$ 14,200
Cost of Acquired Entity, Up Front Cash Consideration			9,400
Future Value of Liabilities Incurred From Business Acquisitions			$ 3,800
Valuation Technique on Contingent Consideration			The fair value of the contingent consideration was measured based on significant inputs not observable in the market (Level 3 inputs). Key assumptions include a discount rate of 5.0% and expected future value of payments of $4.0 million. The $4.0 million of expected future payments was calculated using a probability weighted EBITDA assessment with the highest probability associated with Sofica achieving the targeted EBITDA for each earn-out year.
Acquisition hold-back payment			$ 1,000
Discount rate			5.00%
Contingent Consideration Arrangements, Basis for Amount			The total contingent consideration possible per the stock purchase agreement ranged from zero to $7.5 million. Additionally, the purchase price included a $1.0 million hold-back payment for contingencies as defined in the stock purchase agreement which was paid in the first quarter of 2016.
Contingent Consideration, at fair value			$ 4,000		$ 0		$ 3,153			6,317		$ 0	$ 3,153	$ 6,317
Increase (decrease) in contingent consideration payable									$ 500	$ 600	$ 1,800
CafeX [Member]
Business Acquisition [Line Items]
Equity Method Investment, Ownership Percentage					17.00%		17.20%					17.00%	17.20%
Investments in non-marketable equity investments				$ 1,100	$ 4,300