Goodwill and Other Intangible Assets - Summary of Changes in Carrying Amount of Goodwill by Reportable Segment (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Beginning balance	$ 1,915,690	$ 1,884,920
Acquisitions	10,184	47,800
Acquisition accounting adjustments	502	(353)
Foreign currency translation adjustments	(10,184)	(16,677)
Ending balance	1,916,192	1,915,690
Unified Communications Services [Member]
Goodwill [Line Items]
Beginning balance	873,782	864,568
Acquisitions	0	24,579
Acquisition accounting adjustments	515	0
Foreign currency translation adjustments	(10,317)	(15,365)
Ending balance	863,980	873,782
Safety Services [Member]
Goodwill [Line Items]
Beginning balance	508,679	507,588
Acquisitions	5,277	0
Acquisition accounting adjustments	0	1,091
Foreign currency translation adjustments	0	0
Ending balance	513,956	508,679
Interactive Services [Member]
Goodwill [Line Items]
Beginning balance	244,879	223,014
Acquisitions	4,907	23,221
Acquisition accounting adjustments	(13)	(44)
Foreign currency translation adjustments	133	(1,312)
Ending balance	249,906	244,879
Specialized Agent Services [Member]
Goodwill [Line Items]
Beginning balance	288,350	289,750
Acquisitions	0	0
Acquisition accounting adjustments	0	(1,400)
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
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
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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=73531572&loc=d3e961-128460

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