Business Combinations - Summary of Allocation of Purchase Consideration and Estimated Values of Assets Acquired and Liabilities Assumed (Details) - USD ($)								12 Months Ended
	Aug. 04, 2020	May 27, 2020	Mar. 19, 2020	Feb. 25, 2020	Feb. 07, 2020	Jul. 29, 2019	Apr. 01, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets acquired
Goodwill								$ 187,411,000	$ 91,421,000	$ 48,382,000
Consideration paid
Cash consideration, net of cash acquired								55,138,000	58,419,000	35,857,000
Contingent consideration								10,619,000
Decrease in contingent consideration obligation								(3,665,000)	550,000	$ 250,000
Connexient
Assets acquired
Accounts receivable					$ 849,000
Prepaid expenses and other current assets					518,000
Property and equipment					9,000
Goodwill					14,343,000
Other assets					238,000
Total assets acquired					25,607,000
Liabilities assumed
Accounts payable					751,000
Accrued expenses					208,000
Deferred revenue					2,420,000
Deferred tax liabilities					2,011,000
Other liabilities					211,000
Net assets acquired					20,006,000
Consideration paid
Cash consideration, net of cash acquired								10,991,000
Fair value of common stock issued					9,015,000
Contingent consideration								0
Total					20,200,000			20,006,000
Connexient | Acquired Technology
Assets acquired
Intangible assets other than goodwill					1,220,000
Connexient | Customer Relationships
Assets acquired
Intangible assets other than goodwill					7,800,000
Connexient | Trade Names
Assets acquired
Intangible assets other than goodwill					$ 630,000
CNL Software Limited
Assets acquired
Accounts receivable				$ 1,979,000
Prepaid expenses and other current assets				1,095,000
Property and equipment				731,000
Goodwill				28,679,000
Other assets				1,314,000
Total assets acquired				42,528,000
Liabilities assumed
Accounts payable				315,000
Accrued expenses				1,653,000
Deferred revenue				3,751,000
Deferred tax liabilities				1,553,000
Other liabilities				1,276,000
Net assets acquired				33,980,000
Consideration paid
Cash consideration, net of cash acquired								18,030,000
Fair value of common stock issued				15,950,000
Total				35,700,000				33,980,000
CNL Software Limited | Acquired Technology
Assets acquired
Intangible assets other than goodwill				2,150,000
CNL Software Limited | Customer Relationships
Assets acquired
Intangible assets other than goodwill				5,500,000
CNL Software Limited | Trade Names
Assets acquired
Intangible assets other than goodwill				$ 1,080,000
One2Many Group B.V.
Assets acquired
Accounts receivable			$ 521,000
Other current assets			1,441,000
Property and equipment			19,000
Goodwill			10,704,000
Other assets			176,000
Total assets acquired			17,511,000
Liabilities assumed
Accounts payable			72,000
Accrued expenses			636,000
Deferred revenue			1,460,000
Deferred tax liabilities			985,000
Other current liabilities			136,000
Net assets acquired			14,222,000
Consideration paid
Cash consideration, net of cash acquired								6,563,000
Fair value of common stock issued			5,469,000
Contingent consideration			2,190,000
Decrease in contingent consideration obligation								(8,100,000)
Total			13,100,000					14,222,000
One2Many Group B.V. | Acquired Technology
Assets acquired
Intangible assets other than goodwill			970,000
One2Many Group B.V. | Customer Relationships
Assets acquired
Intangible assets other than goodwill			3,100,000
One2Many Group B.V. | Trade Names
Assets acquired
Intangible assets other than goodwill			$ 580,000
Techwan SA
Assets acquired
Accounts receivable		$ 921,000
Other current assets		235,000
Goodwill		12,678,000
Other assets		254,000
Total assets acquired		20,928,000
Liabilities assumed
Accrued expenses		673,000
Deferred revenue		1,190,000
Deferred tax liabilities		838,000
Other current liabilities		927,000
Net assets acquired		17,300,000
Consideration paid
Cash consideration, net of cash acquired								9,301,000
Fair value of common stock issued		5,074,000
Acquisition-related deferred common stock consideration		895,000
Contingent consideration		2,030,000
Decrease in contingent consideration obligation								2,000,000.0
Total		15,500,000						17,300,000
Techwan SA | Acquired Technology
Assets acquired
Intangible assets other than goodwill		1,160,000
Techwan SA | Customer Relationships
Assets acquired
Intangible assets other than goodwill		5,100,000
Techwan SA | Trade Names
Assets acquired
Intangible assets other than goodwill		$ 580,000
SnapComms Limited
Assets acquired
Accounts receivable	$ 1,808,000
Other current assets	283,000
Property and equipment	118,000
Goodwill	22,629,000
Other assets	943,000
Total assets acquired	42,341,000
Liabilities assumed
Accrued expenses	503,000
Deferred revenue	3,165,000
Deferred tax liabilities	4,960,000
Other liabilities	742,000
Net assets acquired	32,971,000
Consideration paid
Cash consideration, net of cash acquired								10,090,000
Fair value of common stock issued	17,685,000
Acquisition-related deferred common stock consideration	3,149,000
Contingent consideration	2,047,000
Decrease in contingent consideration obligation								2,000,000.0
Total	34,400,000							$ 32,971,000
SnapComms Limited | Acquired Technology
Assets acquired
Intangible assets other than goodwill	2,300,000
SnapComms Limited | Customer Relationships
Assets acquired
Intangible assets other than goodwill	13,300,000
SnapComms Limited | Trade Names
Assets acquired
Intangible assets other than goodwill	$ 960,000
Mission Mode
Assets acquired
Accounts receivable									295,000
Property and equipment									6,000
Goodwill									2,918,000
Other assets									7,000
Total assets acquired									8,356,000
Liabilities assumed
Deferred revenue									880,000
Other liabilities									10,000
Net assets acquired									7,314,000
Accounts payable and accrued expenses									152,000
Consideration paid
Cash consideration, net of cash acquired									6,764,000
Contingent consideration							$ 600,000
Decrease in contingent consideration obligation									550,000
Total							$ 6,800,000		7,314,000
Mission Mode | Acquired Technology
Assets acquired
Intangible assets other than goodwill									310,000
Mission Mode | Customer Relationships
Assets acquired
Intangible assets other than goodwill									4,600,000
Mission Mode | Trade Names
Assets acquired
Intangible assets other than goodwill									220,000
NC4 Inc. and NC4 Public Sector LLC
Assets acquired
Accounts receivable									2,611,000
Other current assets									530,000
Property and equipment									75,000
Goodwill									40,384,000
Total assets acquired									92,910,000
Liabilities assumed
Deferred revenue									7,540,000
Other current liabilities									917,000
Net assets acquired									84,453,000
Consideration paid
Cash consideration, net of cash acquired									51,655,000
Fair value of common stock issued									32,798,000
Total						$ 84,500,000			84,453,000
NC4 Inc. and NC4 Public Sector LLC | Acquired Technology
Assets acquired
Intangible assets other than goodwill									5,210,000
NC4 Inc. and NC4 Public Sector LLC | Customer Relationships
Assets acquired
Intangible assets other than goodwill									35,490,000
NC4 Inc. and NC4 Public Sector LLC | Trade Names
Assets acquired
Intangible assets other than goodwill									$ 8,610,000