Segment Reporting, Geographic and Customer Information - Financial Information of Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue:
REVENUE	$ 568,430	$ 574,448	$ 571,891	$ 565,490	$ 562,938	$ 568,197	$ 552,319	$ 535,140	$ 2,280,259	$ 2,218,594	$ 2,120,972
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization									192,264	180,537	160,669
Operating Income:
OPERATING INCOME	104,970	$ 124,354	$ 116,433	$ 110,693	116,710	$ 114,946	$ 115,561	$ 114,190	456,450	461,407	451,294
Cash Capital Expenditures:
Cash Capital Expenditures									136,810	130,318	114,260
Assets:
Assets	3,612,279				3,818,075				3,612,279	3,818,075	3,496,644
Continuing Operations [Member]
Assets:
Assets	3,594,607				3,513,470				3,594,607	3,513,470	3,196,595
Assets Held For Sale [Member]
Assets:
Assets	17,672				304,605				17,672	304,605	300,049
Operating Segments [Member] | Unified Communications Services [Member]
Revenue:
REVENUE									1,467,711	1,491,639	1,475,016
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization									83,183	89,448	89,991
Operating Income:
OPERATING INCOME									378,421	364,134	358,590
Cash Capital Expenditures:
Cash Capital Expenditures									60,639	46,860	65,875
Operating Segments [Member] | Unified Communications Services [Member] | Continuing Operations [Member]
Assets:
Assets	1,525,890				1,337,667				1,525,890	1,337,667	1,558,700
Operating Segments [Member] | Safety Services [Member]
Revenue:
REVENUE									281,391	278,317	259,120
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization									50,494	48,115	44,407
Operating Income:
OPERATING INCOME									22,585	30,473	23,907
Cash Capital Expenditures:
Cash Capital Expenditures									23,628	31,706	25,974
Operating Segments [Member] | Safety Services [Member] | Continuing Operations [Member]
Assets:
Assets	786,447				787,889				786,447	787,889	764,561
Operating Segments [Member] | Interactive Services [Member]
Revenue:
REVENUE									265,664	235,481	224,440
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization									30,595	25,075	17,793
Operating Income:
OPERATING INCOME									25,155	35,231	43,554
Cash Capital Expenditures:
Cash Capital Expenditures									22,151	15,121	8,516
Operating Segments [Member] | Interactive Services [Member] | Continuing Operations [Member]
Assets:
Assets	430,793				353,253				430,793	353,253	265,827
Operating Segments [Member] | Specialized Agent Services [Member]
Revenue:
REVENUE									276,983	224,621	170,345
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization									27,992	17,899	8,478
Operating Income:
OPERATING INCOME									30,289	31,569	25,243
Cash Capital Expenditures:
Cash Capital Expenditures									12,632	6,592	2,102
Operating Segments [Member] | Specialized Agent Services [Member] | Continuing Operations [Member]
Assets:
Assets	491,449				443,737				491,449	443,737	164,759
Eliminations [Member]
Revenue:
REVENUE									(11,490)	(11,464)	(7,949)
Cash Capital Expenditures:
Cash Capital Expenditures									17,760	30,039	11,793
Corporate [Member] | Continuing Operations [Member]
Assets:
Assets	$ 360,028				$ 590,924				$ 360,028	$ 590,924	$ 442,748