Goodwill and Other Intangible Assets - Summary of Activity in Goodwill by Reporting Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Goodwill [Line Items]
Balance	$ 1,854,526	$ 1,800,310
Accumulated impairment losses	(37,675)	(37,675)
Net balance	1,816,851	1,762,635
Acquisitions		49,723
Acquisition accounting adjustments		1,013
Foreign currency translation adjustment	(4,598)	3,480
Balance	1,849,928	1,854,526
Accumulated impairment losses	(37,675)	(37,675)
Net balance	1,812,253	1,816,851
Unified Communications [Member]
Goodwill [Line Items]
Balance	967,335	962,982
Accumulated impairment losses
Net balance	967,335	962,982
Acquisitions
Acquisition accounting adjustments		970
Foreign currency translation adjustment	(4,614)	3,383
Balance	962,721	967,335
Accumulated impairment losses
Net balance	962,721	967,335
Communication Services [Member]
Goodwill [Line Items]
Balance	887,191	837,328
Accumulated impairment losses	(37,675)	(37,675)
Net balance	849,516	799,653
Acquisitions		49,723
Acquisition accounting adjustments		43
Foreign currency translation adjustment	16	97
Balance	887,207	887,191
Accumulated impairment losses	(37,675)	(37,675)
Net balance	$ 849,532	$ 849,516