ACQUISITIONS (Narrative) (Details) - USD ($) $ in Thousands				3 Months Ended		9 Months Ended		12 Months Ended
	Feb. 05, 2015	Oct. 16, 2014	Sep. 19, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Business Acquisition [Line Items]
Acquisition/divestiture-related costs				$ 2,421	$ 2,147	$ 6,021	$ 5,838
Central Desktop
Business Acquisition [Line Items]
Acquisition/divestiture-related costs								$ 400
Contingent consideration liability		$ 2,900
Negotiated sales price		25,000
Central Desktop | Developed technology
Business Acquisition [Line Items]
Finite-lived intangible assets, preliminary valuation		$ 6,000
Amortization period (in years)		7 years
Central Desktop | Customer Relationships
Business Acquisition [Line Items]
Finite-lived intangible assets, preliminary valuation		$ 1,100
Amortization period (in years)		10 years
Central Desktop | Non-compete agreements
Business Acquisition [Line Items]
Finite-lived intangible assets, preliminary valuation		$ 1,800
Amortization period (in years)		5 years
Central Desktop | Trade Names
Business Acquisition [Line Items]
Finite-lived intangible assets, preliminary valuation		$ 300
Amortization period (in years)		2 years
TalkPoint
Business Acquisition [Line Items]
Acquisition/divestiture-related costs								$ 400
Contingent consideration liability			$ 6,400
Indemnification asset			1,100
Uncertain tax position			1,100
Negotiated sales price			56,500
TalkPoint | Developed technology
Business Acquisition [Line Items]
Finite-lived intangible assets, preliminary valuation			$ 16,000
Amortization period (in years)			7 years
TalkPoint | Customer Relationships
Business Acquisition [Line Items]
Finite-lived intangible assets, preliminary valuation			$ 9,500
Amortization period (in years)			10 years
TalkPoint | Non-compete agreements
Business Acquisition [Line Items]
Finite-lived intangible assets, preliminary valuation			$ 2,200
Amortization period (in years)			5 years
TalkPoint | Trade Names
Business Acquisition [Line Items]
Finite-lived intangible assets, preliminary valuation			$ 700
Amortization period (in years)			2 years
Modality
Business Acquisition [Line Items]
Acquisition/divestiture-related costs						300
Contingent consideration liability	$ 23,100
Negotiated sales price	17,500
Revenue						9,800
Net loss						$ (1,900)
Modality | Customer Relationships
Business Acquisition [Line Items]
Finite-lived intangible assets, preliminary valuation	4,600
Modality | Other intangibles
Business Acquisition [Line Items]
Finite-lived intangible assets, preliminary valuation	$ 3,200