Other Income (Narrative) (Details) - USD ($)	3 Months Ended				6 Months Ended	9 Months Ended
	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Other Income [Line Items]
Proceeds from Insurance Settlement, Investing Activities						$ 567,000	$ 213,000
Other Nonoperating Income (Expense)	$ 279,000		$ 0			$ 582,000	$ 213,000
Tower in Keene New Hampshire [Member]
Other Income [Line Items]
Proceeds from Insurance Settlement, Investing Activities				$ 208,000
Other Nonoperating Income (Expense)				208,000
Tower in Des Moines Iowa [Member]
Other Income [Line Items]
Proceeds from Insurance Settlement, Investing Activities	290,000	$ 250,000
Other Nonoperating Income (Expense)	$ 290,000	$ 250,000			$ 540,000
Tower Sites In Bellingham Washington [Member]
Other Income [Line Items]
Proceeds from Sale of Property, Plant, and Equipment				1,700,000
Other Nonoperating Income (Expense)				$ 1,400,000