Business Segments - Financial Information of Business Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Revenue:
Revenues	$ 656,896	$ 632,803	$ 1,957,853	$ 1,866,441
Operating Income:
Operating Income (Loss)	117,292	131,947	353,033	373,505
Depreciation and Amortization: (Included in Operating Income)
Depreciation and Amortization	46,308	44,131	135,853	127,916
Capital Expenditures:
Capital Expenditures	34,709	28,961	84,093	72,314
Assets:
Assets	3,452,065		3,452,065		3,227,518
Unified Communications [Member]
Revenue:
Revenues	359,007	352,090	1,088,181	1,030,249
Operating Income:
Operating Income (Loss)	96,345	100,279	293,286	290,760
Depreciation and Amortization: (Included in Operating Income)
Depreciation and Amortization	21,840	21,794	66,323	64,021
Capital Expenditures:
Capital Expenditures	17,489	13,257	39,023	32,599
Assets:
Assets	1,667,295		1,667,295		1,620,444
Communication Services [Member]
Revenue:
Revenues	300,847	283,994	877,811	844,403
Operating Income:
Operating Income (Loss)	20,947	31,668	59,747	82,745
Depreciation and Amortization: (Included in Operating Income)
Depreciation and Amortization	24,468	22,337	69,530	63,895
Capital Expenditures:
Capital Expenditures	15,721	12,678	38,197	32,776
Assets:
Assets	1,439,794		1,439,794		1,379,125
Intersegment Eliminations [Member]
Revenue:
Revenues	(2,958)	(3,281)	(8,139)	(8,211)
Corporate [Member]
Capital Expenditures:
Capital Expenditures	1,499	3,026	6,873	6,939
Assets:
Assets	$ 344,976		$ 344,976		$ 227,949