Property, Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Property, plant and equipment [Abstract]
Total property, plant and equipment	$ 611,685	$ 548,656
Less accumulated amortization and depreciation	246,211	237,902
Property, plant and equipment, net	365,474	310,754
Equipment exchange credit for new equipment purchase	20,307	2,923
Gains from the difference between book value and trade in value	600	1,800
Land [Member]
Property, plant and equipment [Abstract]
Total property, plant and equipment	3,345	3,087
Building and Structures [Member]
Property, plant and equipment [Abstract]
Total property, plant and equipment	75,664	71,934
Building and Structures [Member] | Minimum [Member]
Property, plant and equipment [Abstract]
Estimated useful lives	10 years
Building and Structures [Member] | Maximum [Member]
Property, plant and equipment [Abstract]
Estimated useful lives	40 years
Cable and Wire [Member]
Property, plant and equipment [Abstract]
Total property, plant and equipment	175,833	155,884
Cable and Wire [Member] | Minimum [Member]
Property, plant and equipment [Abstract]
Estimated useful lives	4 years
Cable and Wire [Member] | Maximum [Member]
Property, plant and equipment [Abstract]
Estimated useful lives	40 years
Equipment and Software [Member]
Property, plant and equipment [Abstract]
Total property, plant and equipment	331,374	305,362
Equipment and Software [Member] | Minimum [Member]
Property, plant and equipment [Abstract]
Estimated useful lives	2 years
Equipment and Software [Member] | Maximum [Member]
Property, plant and equipment [Abstract]
Estimated useful lives	16 years 8 months 12 days
Plant in Service [Member]
Property, plant and equipment [Abstract]
Total property, plant and equipment	586,216	536,267
Plant under Construction [Member]
Property, plant and equipment [Abstract]
Total property, plant and equipment	$ 25,469	$ 12,389