Property, Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property, plant and equipment [Abstract]
Total property, plant and equipment	$ 656,661	$ 611,685
Less accumulated amortization and depreciation	247,698	246,211
Property, plant and equipment, net	408,963	365,474
Equipment exchange credit for new equipment purchase	14,533	20,307	2,923
Land [Member]
Property, plant and equipment [Abstract]
Total property, plant and equipment	3,415	3,345
Building and Structures [Member]
Property, plant and equipment [Abstract]
Total property, plant and equipment	96,700	75,664
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	187,293	175,833
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	346,072	331,374
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	633,480	586,216
Plant under Construction [Member]
Property, plant and equipment [Abstract]
Total property, plant and equipment	$ 23,181	$ 25,469