Goodwill and Other Intangible Assets - Summary of Activity in Goodwill by Reporting Segments (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Goodwill [Line Items]
Balance	$ 1,800,310	$ 1,667,071
Accumulated impairment losses	(37,675)	(37,675)
Net balance	1,762,635	1,629,396
Acquisitions	49,723	141,828
Acquisition accounting adjustments	699	(3,023)
Foreign currency translation adjustment	(811)	(5,566)
Balance	1,849,921	1,800,310
Accumulated impairment losses	(37,675)	(37,675)
Net balance	1,812,246	1,762,635
Unified Communications
Goodwill [Line Items]
Balance	962,982	843,558
Net balance	962,982	843,558
Acquisitions		124,989
Acquisition accounting adjustments	970
Foreign currency translation adjustment	(905)	(5,565)
Balance	963,047	962,982
Net balance	963,047	962,982
Communication Services [Member]
Goodwill [Line Items]
Balance	837,328	823,513
Accumulated impairment losses	(37,675)	(37,675)
Net balance	799,653	785,838
Acquisitions	49,723	16,839
Acquisition accounting adjustments	(271)	(3,023)
Foreign currency translation adjustment	94	(1)
Balance	886,874	837,328
Accumulated impairment losses	(37,675)	(37,675)
Net balance	$ 849,199	$ 799,653