Commitments, Contingencies and Derivatives (Swapped Variable Cost for Fixed Cost and Terms of Interest Rate Swap Agreements) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Forward-Starting Interest Rate Swap [Member]
Derivative [Line Items]
Notional Amount	$ 50,000	$ 50,000
Derivative, Fair Value, Net	21	(389)
Forward-Starting Interest Rate Swap [Member] | Contract, One
Derivative [Line Items]
Notional Amount	$ 25,000
Trade Date	Feb. 25, 2015
Maturity Date	Feb. 25, 2018
Fixed Rate Paid	1.54%
Derivative, Fair Value, Net	$ 20	(152)
Forward-Starting Interest Rate Swap [Member] | Contract, Two
Derivative [Line Items]
Notional Amount	$ 25,000
Trade Date	Feb. 25, 2015
Maturity Date	Feb. 25, 2019
Fixed Rate Paid	1.74%
Derivative, Fair Value, Net	$ 1	(237)
Interest rate swaps
Derivative [Line Items]
Notional Amount	$ 43,000	43,000
Derivative, Fair Value, Net		(7,571)	$ (8,372)
Interest rate swaps | Contract, One
Derivative [Line Items]
Notional Amount		$ 10,000
Trade Date		Mar. 18, 2009
Maturity Date		Jun. 30, 2021
Fixed Rate Paid		5.09%
Derivative, Fair Value, Net		$ (527)	(806)
Interest rate swaps | Contract, Two
Derivative [Line Items]
Notional Amount		$ 10,000
Trade Date		Jul. 08, 2009
Maturity Date		Jun. 30, 2029
Fixed Rate Paid		5.84%
Derivative, Fair Value, Net		$ (2,133)	(2,321)
Interest rate swaps | Contract, Three
Derivative [Line Items]
Notional Amount		$ 10,000
Trade Date		May 06, 2010
Maturity Date		Jun. 30, 2030
Fixed Rate Paid		5.71%
Derivative, Fair Value, Net		$ (2,129)	(2,290)
Interest rate swaps | Contract, Four
Derivative [Line Items]
Notional Amount		$ 5,000
Trade Date		Mar. 14, 2011
Maturity Date		Mar. 30, 2031
Fixed Rate Paid		4.35%
Derivative, Fair Value, Net		$ (1,137)	(1,211)
Interest rate swaps | Contract, Five
Derivative [Line Items]
Notional Amount		$ 8,000
Trade Date		May 04, 2011
Maturity Date		Jul. 07, 2031
Fixed Rate Paid		4.14%
Derivative, Fair Value, Net		$ (1,645)	$ (1,744)