Financial Instruments and Fair Values - Gain and Loss of Cash Flow Hedges (Details) - Cash Flow Hedging [Member] - Designated as Hedging Instrument [Member] - Interest rate swaps [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in other comprehensive income (loss) - effective portion	$ (3,054)	$ (1,922)
Amount of gain (loss) reclassified from accumulated other comprehensive income (loss) into interest expense - effective portion	0	0
Amount of gain (loss) recognized in other Income/expense - ineffective portion	$ 0	$ 0