Defined Benefit Pension Plans Multiemployer Pension Plans (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Multiemployer Plans [Line Items]
Multiemployer Plan, Period Contributions	$ 492	$ 503	$ 427
National Electric Benefit Fund [Member]
Multiemployer Plans [Line Items]
Number of collective-bargaining agreements	7
Multiemployer Plan, Period Contributions	417	442	380
Eighth District Electrical Pension Fund [Member]
Multiemployer Plans [Line Items]
Number of collective-bargaining agreements	1
Multiemployer Plan, Period Contributions	$ 75	$ 60	$ 47