Accounts Receivable, Net - Schedule of Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning of period balance	$ (4,696)
(Provision for) / recovery of expected credit losses	(32)	$ (1,885)
End of period balance	(3,912)
Alarm.com and Certain Subsidiaries
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning of period balance	(4,442)	(2,500)
(Provision for) / recovery of expected credit losses	(36)	(1,886)
Write-offs	808	43
End of period balance	(3,670)	(4,555)
Alarm.com and Certain Subsidiaries | Impact of adopting Topic 326
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning of period balance		(212)
All Other Subsidiaries
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning of period balance	(254)	(84)
(Provision for) / recovery of expected credit losses	4	1
Write-offs	8	4
End of period balance	$ (242)	(234)
All Other Subsidiaries | Impact of adopting Topic 326
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning of period balance		$ (155)