Segment Reporting, Geographic and Customer Information - Geographic Information by Organizational Region for Revenue and Long-lived Assets (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
Long-Lived Assets:
Long-Lived Assets	2,746,543				2,812,045				2,746,543	2,812,045	2,808,918
Operating Segments [Member] | Unified Communications Services [Member]
Revenue:
REVENUE									1,425,281	1,467,711	1,491,639
Operating Segments [Member] | Safety Services [Member]
Revenue:
REVENUE									296,320	281,391	278,317
Operating Segments [Member] | Interactive Services [Member]
Revenue:
REVENUE									300,739	265,664	235,481
Operating Segments [Member] | Specialized Agent Services [Member]
Revenue:
REVENUE									281,542	276,983	224,621
Eliminations [Member]
Revenue:
REVENUE									(11,919)	(11,490)	(11,464)
Americas-United States [Member]
Revenue:
REVENUE									1,833,548	1,812,068	1,716,667
Long-Lived Assets:
Long-Lived Assets	2,546,361				2,593,739				2,546,361	2,593,739	2,612,394
Americas-United States [Member] | Operating Segments [Member] | Unified Communications Services [Member]
Revenue:
REVENUE									982,319	1,010,262	1,002,157
Americas-United States [Member] | Operating Segments [Member] | Safety Services [Member]
Revenue:
REVENUE									290,620	276,262	271,278
Americas-United States [Member] | Operating Segments [Member] | Interactive Services [Member]
Revenue:
REVENUE									290,986	260,051	230,075
Americas-United States [Member] | Operating Segments [Member] | Specialized Agent Services [Member]
Revenue:
REVENUE									281,542	276,983	224,621
Americas-United States [Member] | Eliminations [Member]
Revenue:
REVENUE									(11,919)	(11,490)	(11,464)
Europe, Middle East & Africa [Member]
Revenue:
REVENUE									295,599	310,805	324,466
Long-Lived Assets:
Long-Lived Assets	172,439				195,203				172,439	195,203	176,817
Europe, Middle East & Africa [Member] | Operating Segments [Member] | Unified Communications Services [Member]
Revenue:
REVENUE									292,843	308,841	323,173
Europe, Middle East & Africa [Member] | Operating Segments [Member] | Safety Services [Member]
Revenue:
REVENUE									84	34	3
Europe, Middle East & Africa [Member] | Operating Segments [Member] | Interactive Services [Member]
Revenue:
REVENUE									2,672	1,930	1,290
Europe, Middle East & Africa [Member] | Operating Segments [Member] | Specialized Agent Services [Member]
Revenue:
REVENUE									0	0	0
Europe, Middle East & Africa [Member] | Eliminations [Member]
Revenue:
REVENUE									0	0	0
Asia Pacific [Member]
Revenue:
REVENUE									143,601	141,849	153,628
Long-Lived Assets:
Long-Lived Assets	18,495				21,151				18,495	21,151	17,891
Asia Pacific [Member] | Operating Segments [Member] | Unified Communications Services [Member]
Revenue:
REVENUE									140,703	138,595	150,028
Asia Pacific [Member] | Operating Segments [Member] | Safety Services [Member]
Revenue:
REVENUE									632	303	300
Asia Pacific [Member] | Operating Segments [Member] | Interactive Services [Member]
Revenue:
REVENUE									2,266	2,951	3,300
Asia Pacific [Member] | Operating Segments [Member] | Specialized Agent Services [Member]
Revenue:
REVENUE									0	0	0
Asia Pacific [Member] | Eliminations [Member]
Revenue:
REVENUE									0	0	0
America-Other [Member]
Revenue:
REVENUE									19,215	15,537	23,833
Long-Lived Assets:
Long-Lived Assets	$ 9,248				$ 1,952				9,248	1,952	1,816
America-Other [Member] | Operating Segments [Member] | Unified Communications Services [Member]
Revenue:
REVENUE									9,416	10,013	16,281
America-Other [Member] | Operating Segments [Member] | Safety Services [Member]
Revenue:
REVENUE									4,984	4,792	6,736
America-Other [Member] | Operating Segments [Member] | Interactive Services [Member]
Revenue:
REVENUE									4,815	732	816
America-Other [Member] | Operating Segments [Member] | Specialized Agent Services [Member]
Revenue:
REVENUE									0	0	0
America-Other [Member] | Eliminations [Member]
Revenue:
REVENUE									$ 0	$ 0	$ 0