Lease Commitments (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Future minimum payments under non-cancelable agreements [Abstract]
2013	$ 11,648,000
2014	11,531,000
2015	11,287,000
2016	10,899,000
2017	10,939,000
2018 and beyond	60,489,000
Total future lease payments	116,793,000
Rent expense	13,100,000	12,400,000	11,200,000
Operating Leases, Future Minimum Payments Receivable [Abstract]
2013	5,169,000
2014	4,750,000
2015	4,237,000
2016	2,405,000
2017	1,400,000
2018 and beyond	9,334,000
Total minimum rental receipts	27,295,000
Rent income	$ 6,100,000	$ 6,100,000	$ 6,100,000
Towers [Member]
Operating Leased Assets [Line Items]
Number of renewals	4
Term of renewals	5 years
Towers [Member] | Minimum [Member]
Operating Leased Assets [Line Items]
Terms of leases	5 years
Towers [Member] | Maximum [Member]
Operating Leased Assets [Line Items]
Terms of leases	10 years
Other [Member] | Minimum [Member]
Operating Leased Assets [Line Items]
Terms of leases	5 years
Other [Member] | Maximum [Member]
Operating Leased Assets [Line Items]
Terms of leases	20 years