Fair Value Measurements and Derivative Instruments Reporting (Fair value and basis of valuation of financial liabilities) (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Level 1 [Member] | Interest Rate Swap Asset [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets	$ 0	$ 0
Level 1 [Member] | Interest Rate Swap Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities	0	0
Level 2 [Member] | Interest Rate Swap Asset [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets	275	0
Level 2 [Member] | Interest Rate Swap Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities	0	(129)
Level 3 [Member] | Interest Rate Swap Asset [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets	0	0
Level 3 [Member] | Interest Rate Swap Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities	$ 0	$ 0