Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($) Customer	Sep. 30, 2019 USD ($) Customer	Sep. 30, 2020 USD ($) Customer Vendor	Sep. 30, 2019 USD ($) Customer	Dec. 31, 2019 USD ($) Customer
Summary Of Significant Accounting Policies [Line Items]
Equity method investments	$ 0		$ 0		$ 0
Guarantee or other funding obligations under equity method investment	341,073,000		341,073,000		343,464,000
Earnings or losses from equity method investment	0	$ 0	0	$ 0
Revenue recognized from customer contracts	752,000		5,692,000
Remaining deferred revenues recognized			1,900,000
Note payable - related party	$ 1,332,000		$ 1,332,000		$ 1,275,000
Number of customers with revenues greater than 10% | Customer	0	0	0	0
Number of customers with accounts receivable greater than 10% | Customer					0
Revenues	$ 60,623,000	$ 67,707,000	$ 182,626,000	$ 197,552,000
Inventories finished goods and purchased parts	27,775,000		27,775,000		$ 33,379,000
Inventories raw materials	6,464,000		6,464,000		$ 6,502,000
Equity Method Investment, Guarantee or Other Funding [Member]
Summary Of Significant Accounting Policies [Line Items]
Guarantee or other funding obligations under equity method investment	$ 0	$ 0	$ 0	$ 0
Carrier Corporation [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of customers with accounts receivable greater than 10% | Customer	1
Carrier Corporation [Member] | Accounts Receivable [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage	16.80%
Sanmina Corporation [Member] | Customer Concentration Risk [Member] | Revenues [Member] | Mexico [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage	77.00%	66.20%	84.60%	65.40%
Number of vendors | Vendor			1
Revenues	$ 16,935,000	$ 18,974,000	$ 55,829,000	$ 54,286,000
Maximum [Member] | Revenues [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage	10.00%	10.00%	10.00%	10.00%
Maximum [Member] | Accounts Receivable [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage					10.00%
ASU 2014-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Warranty period			1 year
Estimated life of communicator			3 years
ASU 2014-09 [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Additional term of the agreement			2 years
ASU 2014-09 [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Additional term of the agreement			5 years