Schedule II - Valuation and Qualifying Accounts (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Allowance for Excess or Obsolete System Components
Valuation and qualifying accounts
Balance Beginning of Period	$ 1,054	$ 1,197	$ 845
Additions Charged to Costs and Expenses	1,467	1,275	1,163
Deductions	1,245	1,418	811
Balance End of Period	1,276	1,054	1,197
Allowance for Doubtful Accounts
Valuation and qualifying accounts
Balance Beginning of Period	437	409	652
Additions Charged to Costs and Expenses	481	534	636
Deductions	668	506	879
Balance End of Period	250	437	409
Allowance for System Removal
Valuation and qualifying accounts
Balance Beginning of Period	1,292	994	896
Additions Charged to Costs and Expenses	3,782	5,012	4,399
Deductions	4,080	4,714	4,301
Balance End of Period	994	1,292	994
Deferred Tax Valuation Allowance
Valuation and qualifying accounts
Balance Beginning of Period	232,368	237,848	221,665
Additions Related to Other Accounts	19,872		16,183
Deductions		5,480
Balance End of Period	$ 252,240	$ 232,368	$ 237,848