Derivative Instruments - Schedule of Gain or Loss Recognized on Interest Rate Derivatives Designated as Cash Flow Hedges (Details) - Cash flow hedging - Designated as hedging instrument - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Interest Rate Cash Flow Hedges [Roll Forward]
Balance at beginning of period	$ (5,963)	$ (10,079)	$ (7,462)	$ (11,706)
Amount of (loss) gain recognized in cumulative other comprehensive loss	(418)	537	(1,378)	(324)
Amount of loss reclassified from cumulative other comprehensive loss into interest expense	1,239	1,268	3,698	3,756
Unrealized gain on derivative instruments	821	1,805	2,320	3,432
Balance at end of period	$ (5,142)	$ (8,274)	$ (5,142)	$ (8,274)