Goodwill and Other Intangible Assets - Summary of Changes in Carrying Amount of Goodwill by Reportable Segment (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2017	Dec. 31, 2016
Goodwill [Line Items]
Beginning balance	$ 1,916,192	$ 1,915,690
Acquisitions	18,316	10,184
Acquisition accounting adjustments	(446)	502
Foreign currency translation adjustments	13,770	(10,184)
Ending balance	1,947,832	1,916,192
Unified Communications Services [Member]
Goodwill [Line Items]
Beginning balance	863,980	873,782
Acquisitions	1,207	0
Acquisition accounting adjustments	0	515
Foreign currency translation adjustments	13,085	(10,317)
Ending balance	878,272	863,980
Safety Services [Member]
Goodwill [Line Items]
Beginning balance	513,956	508,679
Acquisitions	0	5,277
Acquisition accounting adjustments	(273)	0
Foreign currency translation adjustments	0	0
Ending balance	513,683	513,956
Interactive Services [Member]
Goodwill [Line Items]
Beginning balance	249,906	244,879
Acquisitions	17,109	4,907
Acquisition accounting adjustments	(173)	(13)
Foreign currency translation adjustments	685	133
Ending balance	267,527	249,906
Specialized Agent Services [Member]
Goodwill [Line Items]
Beginning balance	288,350	288,350
Acquisitions	0	0
Acquisition accounting adjustments	0	0
Foreign currency translation adjustments	0	0
Ending balance	$ 288,350	$ 288,350

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
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-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 16
-URI http://asc.fasb.org/extlink&oid=84229725&loc=d3e961-128460

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