Other Income (Narrative) (Details) - USD ($)	3 Months Ended						12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Other Income [Line Items]
Proceeds from Insurance Settlement, Investing Activities							$ 589,000	$ 233,000
Other Nonoperating Income (Expense)	$ 52,000	$ 279,000	$ 31,000	$ 272,000	$ 20,000	$ 213,000	634,000	$ 233,000	$ 16,000
Tower in Keene New Hampshire [Member]
Other Income [Line Items]
Gain (Loss) On Insurance Settlement						208,000
Proceeds from Insurance Settlement, Investing Activities						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
Gain (Loss) on Disposition of Property Plant Equipment						$ 1,400,000