Derivatives and Hedging Activities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Details of derivative positions for interest rate swaps which qualify as hedges for accounting purposes
Notional Amount	$ 200,000	$ 200,000
Fair Value	(11,921)	(16,189)
Positions One [Member]
Details of derivative positions for interest rate swaps which qualify as hedges for accounting purposes
Notional Amount	25,000	25,000
Trade Date	Feb. 16, 2006	Feb. 16, 2006
Effective Date	Dec. 28, 2006	Dec. 28, 2006
Maturity Date	Dec. 28, 2016	Dec. 28, 2016
Receive (Variable) Index	3 Month LIBOR	3 Month LIBOR
Current Rate Received	0.27%	0.31%
Pay Fixed Swap Rate	5.04%	5.04%
Fair Value	(3,562)	(4,416)
Positions Two [Member]
Details of derivative positions for interest rate swaps which qualify as hedges for accounting purposes
Notional Amount	25,000	25,000
Trade Date	Feb. 16, 2006	Feb. 16, 2006
Effective Date	Dec. 28, 2006	Dec. 28, 2006
Maturity Date	Dec. 28, 2016	Dec. 28, 2016
Receive (Variable) Index	3 Month LIBOR	3 Month LIBOR
Current Rate Received	0.27%	0.31%
Pay Fixed Swap Rate	5.04%	5.04%
Fair Value	(3,563)	(4,417)
Positions Three [Member]
Details of derivative positions for interest rate swaps which qualify as hedges for accounting purposes
Notional Amount	25,000	25,000
Trade Date	Dec. 08, 2008	Dec. 08, 2008
Effective Date	Dec. 10, 2008	Dec. 10, 2008
Maturity Date	Dec. 10, 2013	Dec. 10, 2013
Receive (Variable) Index	3 Month LIBOR	3 Month LIBOR
Current Rate Received	0.27%	0.31%
Pay Fixed Swap Rate	2.65%	2.65%
Fair Value	(264)	(553)
Positions Four [Member]
Details of derivative positions for interest rate swaps which qualify as hedges for accounting purposes
Notional Amount	25,000	25,000
Trade Date	Dec. 09, 2008	Dec. 09, 2008
Effective Date	Dec. 10, 2008	Dec. 10, 2008
Maturity Date	Dec. 10, 2013	Dec. 10, 2013
Receive (Variable) Index	3 Month LIBOR	3 Month LIBOR
Current Rate Received	0.27%	0.31%
Pay Fixed Swap Rate	2.59%	2.59%
Fair Value	(258)	(539)
Positions Five [Member]
Details of derivative positions for interest rate swaps which qualify as hedges for accounting purposes
Notional Amount	25,000	25,000
Trade Date	Dec. 09, 2008	Dec. 09, 2008
Effective Date	Dec. 10, 2008	Dec. 10, 2008
Maturity Date	Dec. 10, 2018	Dec. 10, 2018
Receive (Variable) Index	3 Month LIBOR	3 Month LIBOR
Current Rate Received	0.27%	0.31%
Pay Fixed Swap Rate	2.94%	2.94%
Fair Value	(1,719)	(2,819)
Positions Six [Member]
Details of derivative positions for interest rate swaps which qualify as hedges for accounting purposes
Notional Amount	50,000	50,000
Trade Date	Nov. 17, 2009	Nov. 17, 2009
Effective Date	Dec. 20, 2010	Dec. 20, 2010
Maturity Date	Dec. 20, 2014	Dec. 20, 2014
Receive (Variable) Index	3 Month LIBOR	3 Month LIBOR
Current Rate Received	0.27%	0.31%
Pay Fixed Swap Rate	3.04%	3.04%
Fair Value	(1,955)	(2,647)
Positions Seven [Member]
Details of derivative positions for interest rate swaps which qualify as hedges for accounting purposes
Notional Amount	25,000	25,000
Trade Date	May 05, 2011	May 05, 2011
Effective Date	Jun. 10, 2011	Jun. 10, 2011
Maturity Date	Jun. 10, 2015	Jun. 10, 2015
Receive (Variable) Index	3 Month LIBOR	3 Month LIBOR
Current Rate Received	0.27%	0.31%
Pay Fixed Swap Rate	1.71%	1.71%
Fair Value	$ (600)	$ (798)