Goodwill and Intangible Assets - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended
	Dec. 31, 2020	Mar. 31, 2021	Sep. 30, 2020	Mar. 31, 2020
Business Acquisition [Line Items]
Amortization expense		$ 200		$ 200
FCC spectrum licenses
Business Acquisition [Line Items]
Indefinite-lived intangible assets acquired			$ 16,100
Canaan Cable
Business Acquisition [Line Items]
Aggregate purchase price	$ 2,100
Property, plant and equipment acquired	1,100
Goodwill	600
Remitted portion of acquisition price	1,890
Subscriber relationships | Canaan Cable
Business Acquisition [Line Items]
Subscriber relationship acquired	$ 400