Acquisitions - Additional Information (Detail) - USD ($) $ in Thousands										1 Months Ended	12 Months Ended
		Dec. 09, 2016	Mar. 14, 2016	Nov. 02, 2015	Jun. 01, 2015	Nov. 03, 2014	Sep. 02, 2014	Jun. 13, 2014	Apr. 21, 2014	Oct. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Purchase price of acquisition											$ 19,920	$ 94,376	$ 398,060
Purchase price allocation, goodwill recorded											1,916,192	1,915,690	1,884,920
Contingent consideration arrangement											1,099	234	0
Total acquisition costs expensed											3,700	3,100	3,500
Revenue during 12 months subsequent to acquisition											$ 24,200	71,900	$ 74,700
911 ETC [Member]
Business Acquisition [Line Items]
Date of acquisition											Dec. 09, 2016
Purchase price of acquisition		$ 10,200
Purchase price allocation, goodwill recorded		5,277
Preliminary purchase price allocation, intangible assets recorded		$ 6,484
Synrevoice [Member]
Business Acquisition [Line Items]
Date of acquisition											Mar. 14, 2016
Purchase price of acquisition			$ 9,300
Purchase price allocation, goodwill recorded			4,893
Preliminary purchase price allocation, intangible assets recorded			$ 6,455
ClientTell [Member]
Business Acquisition [Line Items]
Date of acquisition											Nov. 02, 2015
Purchase price of acquisition				$ 38,400
Purchase price allocation, goodwill recorded	[1]			15,004
Preliminary purchase price allocation, intangible assets recorded				26,300
Additional cash to be paid				$ 10,500
Additional cash to be paid over the period in years				5 years
Contingent consideration arrangement				$ 5,400							$ 4,600	$ 5,600
Business acquisition contingent consideration paid											$ 2,100
Magnetic North [Member]
Business Acquisition [Line Items]
Date of acquisition											Oct. 31, 2015
Purchase price of acquisition										$ 39,200
Purchase price allocation, goodwill recorded										25,094
Preliminary purchase price allocation, intangible assets recorded										$ 16,361
Sharp School [Member]
Business Acquisition [Line Items]
Date of acquisition											Jun. 01, 2015
Purchase price of acquisition					$ 17,200
Purchase price allocation, goodwill recorded					8,203
Preliminary purchase price allocation, intangible assets recorded					$ 9,092
School Reach [Member]
Business Acquisition [Line Items]
Date of acquisition											Nov. 03, 2014
Purchase price of acquisition						$ 13,500
Purchase price allocation, goodwill recorded						6,923
Preliminary purchase price allocation, intangible assets recorded						7,350
Working capital adjustment						$ 1,000
911 Enable [Member]
Business Acquisition [Line Items]
Date of acquisition											Sep. 02, 2014
Purchase price of acquisition							$ 42,400
Purchase price allocation, goodwill recorded							21,289
Preliminary purchase price allocation, intangible assets recorded							$ 20,685
Health Advocate [Member]
Business Acquisition [Line Items]
Date of acquisition											Jun. 13, 2014
Purchase price of acquisition								$ 265,900
Purchase price allocation, goodwill recorded								156,014
Preliminary purchase price allocation, intangible assets recorded								$ 151,990
School Messenger [Member]
Business Acquisition [Line Items]
Date of acquisition											Apr. 21, 2014
Purchase price of acquisition									$ 77,400
Purchase price allocation, goodwill recorded									50,386
Preliminary purchase price allocation, intangible assets recorded									$ 40,145

[1] 15.0