Acquisitions - Additional Information (Detail) - USD ($) $ in Thousands					3 Months Ended		6 Months Ended
	May 02, 2017	Mar. 07, 2017	Dec. 09, 2016	Mar. 14, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Purchase price of acquisition							$ 29,882	$ 9,745
Purchase price allocation, goodwill recorded					$ 1,947,832		1,947,832		$ 1,916,192	$ 1,915,690
Total acquisition costs expensed					1,500	$ 1,400	2,800	2,500
Revenue					$ 5,100	$ 1,000	$ 7,400	$ 1,200
Callpointe.com, Inc. [Member]
Business Acquisition [Line Items]
Date of acquisition							May 02, 2017
Purchase price of acquisition	$ 25,900
Purchase price allocation, goodwill recorded	17,109
Purchase price allocation, intangible assets recorded	$ 12,690
Vocus [Member]
Business Acquisition [Line Items]
Date of acquisition							Mar. 07, 2017
Purchase price of acquisition		$ 4,000
Purchase price allocation, goodwill recorded		1,206
Purchase price allocation, intangible assets recorded		$ 685
911 ETC [Member]
Business Acquisition [Line Items]
Date of acquisition							Dec. 09, 2016
Purchase price of acquisition			$ 10,200
Purchase price allocation, goodwill recorded			5,004
Purchase price allocation, intangible assets recorded			$ 6,484
Synrevoice [Member]
Business Acquisition [Line Items]
Date of acquisition							Mar. 14, 2016
Purchase price of acquisition				$ 9,200
Purchase price allocation, goodwill recorded				4,720
Purchase price allocation, intangible assets recorded				$ 6,455
Apollo Global Management, LLC [Member]
Business Acquisition [Line Items]
Total acquisition costs expensed							$ 4,400