Other Accrued Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Components of other accrued liabilities
Accrued systems rental and maintenance costs	$ 2,626	$ 2,768
Accrued site rental fees	1,164	1,202
Accrued property and sales taxes payable	11,515	11,561
Accrued self-insurance expense	1,178	1,299
Deferred gain on sale of equipment	324	1,293
Other accrued expenses	6,556	8,712
Total	$ 23,363	$ 26,835