Derivative Instruments (Details 1) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative Instruments [Abstract]
Hedging losses included in accumulated other comprehensive income	$ 1,137,000
Loss (gain) on derivatives, net	(1,495,000)	4,470,000	(1,825,000)
Senior unsecured notes	$ 7,766,251,000	$ 7,379,308,000