Business Segments - Financial Information of Business Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Revenue:
Revenues	$ 660,224	$ 639,062
Operating Income:
Operating Income	93,290	114,242
Depreciation and Amortization (Included in Operating Income):
Depreciation and Amortization	44,357	43,315
Capital Expenditures:
Capital Expenditures	23,301	23,876
Assets:
Assets	3,940,932		3,448,153
Unified Communications [Member]
Revenue:
Revenues	367,568	359,647
Operating Income:
Operating Income	77,865	97,136
Depreciation and Amortization (Included in Operating Income):
Depreciation and Amortization	21,672	22,346
Capital Expenditures:
Capital Expenditures	11,181	9,109
Assets:
Assets	1,629,471		1,629,019
Communication Services [Member]
Revenue:
Revenues	296,451	281,737
Operating Income:
Operating Income	15,425	17,106
Depreciation and Amortization (Included in Operating Income):
Depreciation and Amortization	22,685	20,969
Capital Expenditures:
Capital Expenditures	11,221	11,535
Assets:
Assets	1,400,586		1,437,695
Corporate [Member]
Capital Expenditures:
Capital Expenditures	899	3,232
Assets:
Assets	910,875		381,439
Intersegment Eliminations [Member]
Revenue:
Revenues	$ (3,795)	$ (2,322)