Accounts Receivable, Net - Schedule of Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201613Member		us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201602Member
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning of period balance		$ (2,584)		$ (2,584)
Provision for / (recovery of) expected credit losses	$ 900		$ (200)	(965)	$ (460)
End of period balance	(3,788)			(3,788)
Alarm.com and Certain Subsidiaries
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning of period balance	(4,555)	(2,500)		(2,500)
Provision for / (recovery of) expected credit losses	935			(951)
Write-offs	70			113
End of period balance	(3,550)	(4,555)		(3,550)
Alarm.com and Certain Subsidiaries | Impact of adopting Topic 326
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning of period balance	0	(212)		(212)
End of period balance		0
All Other Subsidiaries
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning of period balance	(234)	(84)		(84)
Provision for / (recovery of) expected credit losses	(15)			(14)
Write-offs	11			15
End of period balance	(238)	(234)		(238)
All Other Subsidiaries | Impact of adopting Topic 326
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning of period balance	$ 0	(155)		$ (155)
End of period balance		$ 0