Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 State	Dec. 31, 2013	Dec. 31, 2012
Description of business [Abstract]
Non Sprint operations, number of states	4
Cash and cash equivalents:
Cash equivalents	$ 40,000,000	$ 20,000,000
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of year	924,000	1,113,000	838,000
Bad debt expense	1,678,000	2,019,000	2,870,000
Losses charged to allowance	(2,218,000)	(2,390,000)	(2,854,000)
Recoveries added to allowance	378,000	182,000	259,000
Balance at end of year	762,000	924,000	1,113,000
Asset Retirement Obligation [Roll Forward]
Balance at beginning of year	6,485,000	5,896,000	7,610,000
Additional liabilities accrued	403,000	1,189,000	1,148,000
Changes to prior estimates	0	0	(2,265,000)
Payments made	(334,000)	(909,000)	(846,000)
Accretion expense	374,000	309,000	249,000
Balance at end of year	$ 6,928,000	$ 6,485,000	$ 5,896,000
Minimum [Member]
Description of business [Abstract]
Megahertz spectrum used	800
Investments: [Abstract]
Ownership percentage to consider Investments Carried at Equity Method Investments (in hundredths)	20.00%
Maximum [Member]
Description of business [Abstract]
Megahertz spectrum used	1,900
Investments: [Abstract]
Ownership percentage to consider Investments Carried at Cost (in hundredths)	20.00%
Ownership percentage to consider Investments Carried at Equity Method Investments (in hundredths)	50.00%