Segment Reporting, Geographic and Customer Information - Financial Information of Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue:
REVENUE	$ 567,380	$ 571,407	$ 582,397	$ 570,779	$ 568,430	$ 574,448	$ 571,891	$ 565,490	$ 2,291,963	$ 2,280,259	$ 2,218,594
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization									194,682	192,264	180,537
Operating Income:
OPERATING INCOME	102,690	$ 109,499	$ 123,101	$ 108,924	104,970	$ 124,354	$ 116,433	$ 110,693	444,214	456,450	461,407
Cash Capital Expenditures:
Cash Capital Expenditures									126,581	136,810	130,318
Assets:
Assets	3,440,838				3,555,217				3,440,838	3,555,217	3,743,916
Continuing Operations [Member]
Assets:
Assets	3,440,838				3,537,545				3,440,838	3,537,545	3,439,311
Assets Held For Sale [Member]
Assets:
Assets	0				17,672				0	17,672	304,605
Operating Segments [Member] | Unified Communications Services [Member]
Revenue:
REVENUE									1,425,281	1,467,711	1,491,639
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization									82,371	83,183	89,448
Operating Income:
OPERATING INCOME									327,195	377,850	366,438
Cash Capital Expenditures:
Cash Capital Expenditures									42,854	60,639	46,860
Operating Segments [Member] | Unified Communications Services [Member] | Continuing Operations [Member]
Assets:
Assets	1,459,919				1,525,890				1,459,919	1,525,890	1,337,667
Operating Segments [Member] | Safety Services [Member]
Revenue:
REVENUE									296,320	281,391	278,317
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization									44,668	50,494	48,115
Operating Income:
OPERATING INCOME									54,703	22,408	31,052
Cash Capital Expenditures:
Cash Capital Expenditures									31,339	23,628	31,706
Operating Segments [Member] | Safety Services [Member] | Continuing Operations [Member]
Assets:
Assets	772,308				786,447				772,308	786,447	787,889
Operating Segments [Member] | Interactive Services [Member]
Revenue:
REVENUE									300,739	265,664	235,481
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization									37,395	30,595	25,075
Operating Income:
OPERATING INCOME									30,631	25,044	35,604
Cash Capital Expenditures:
Cash Capital Expenditures									22,197	22,151	15,121
Operating Segments [Member] | Interactive Services [Member] | Continuing Operations [Member]
Assets:
Assets	430,722				430,793				430,722	430,793	353,253
Operating Segments [Member] | Specialized Agent Services [Member]
Revenue:
REVENUE									281,542	276,983	224,621
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization									30,248	27,992	17,899
Operating Income:
OPERATING INCOME									16,438	30,468	31,858
Cash Capital Expenditures:
Cash Capital Expenditures									11,109	12,632	6,592
Operating Segments [Member] | Specialized Agent Services [Member] | Continuing Operations [Member]
Assets:
Assets	468,384				491,449				468,384	491,449	443,737
Eliminations [Member]
Revenue:
REVENUE									(11,919)	(11,490)	(11,464)
Corporate Other-Unallocated [Member]
Operating Income:
OPERATING INCOME									15,247	680	(3,545)
Cash Capital Expenditures:
Cash Capital Expenditures									19,082	17,760	30,039
Corporate Other-Unallocated [Member] | Continuing Operations [Member]
Assets:
Assets	$ 309,505				$ 302,966				$ 309,505	$ 302,966	$ 516,765