Financial Instruments: Derivatives and Hedging (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Financial Instruments: Derivatives and Hedging
Fair Value	$ 0		$ 0		$ 204,000
Derivative, Fair Value, Net	(3,036,000)		(3,036,000)
Gain (loss) from changes in fair value	500,000	$ 100,000	500,000	$ 100,000
Fair value of derivatives in a net liability position	3,100,000		3,100,000
Aggregate termination value	3,200,000		3,200,000
Estimated current balance held in accumulated other comprehensive loss to be reclassified into earnings within the next 12 months			4,500,000
Share of joint venture of accumulated other comprehensive loss reclassified into equity in net income from unconsolidated joint ventures within the next 12 months			1,800,000
Amount of (Loss) Gain Recognized in Other Comprehensive Loss (Effective Portion)	(4,191,000)	(818,000)	(13,875,000)	(9,576,000)
Amount of Loss Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	5,035,000	3,068,000	7,549,000	6,146,000
Amount of (Loss) or Gain Recognized into Income (Ineffective Portion)	(599,000)	2,000	(1,074,000)	(424,000)
Joint venture
Financial Instruments: Derivatives and Hedging
Amount of (Loss) Gain Recognized in Other Comprehensive Loss (Effective Portion)	(3,005,000)	277,000	(5,770,000)	(960,000)
Amount of Loss Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	567,000	331,000	918,000	662,000
Amount of (Loss) or Gain Recognized into Income (Ineffective Portion)	(600,000)	16,000	(1,036,000)	0
Interest Rate Swap Expiring in December 2017
Financial Instruments: Derivatives and Hedging
Notional Value	$ 200,000,000		$ 200,000,000
Strike Rate (as a percent)	0.9375%		0.9375%
Fair Value	$ (1,202,000)		$ (1,202,000)
Interest Rate Swap Expiring in December 2017
Financial Instruments: Derivatives and Hedging
Notional Value	$ 150,000,000		$ 150,000,000
Strike Rate (as a percent)	0.94%		0.94%
Fair Value	$ (906,000)		$ (906,000)
Interest Rate Swap Expiring in December 2017
Financial Instruments: Derivatives and Hedging
Notional Value	$ 150,000,000		$ 150,000,000
Strike Rate (as a percent)	0.94%		0.94%
Fair Value	$ (906,000)		$ (906,000)
Interest Rate Cap Expiring October 2016
Financial Instruments: Derivatives and Hedging
Notional Value	$ 117,392,000		$ 117,392,000
Strike Rate (as a percent)	6.00%		6.00%
Fair Value	$ 0		$ 0
Interest Rate Swap Expiring in January 2017
Financial Instruments: Derivatives and Hedging
Notional Value	$ 14,409,000		$ 14,409,000
Strike Rate (as a percent)	0.50%		0.50%
Fair Value	$ (4,000)		$ (4,000)
Interest Rate Swap Expiring in February 2017
Financial Instruments: Derivatives and Hedging
Notional Value	$ 8,018,000		$ 8,018,000
Strike Rate (as a percent)	0.852%		0.852%
Fair Value	$ (18,000)		$ (18,000)
Interest Rate Cap Expiring in September 2017
Financial Instruments: Derivatives and Hedging
Notional Value	$ 137,500,000		$ 137,500,000
Strike Rate (as a percent)	4.00%		4.00%
Fair Value	$ 0		$ 0
Interest Rate Cap Expiring in May 2017
Financial Instruments: Derivatives and Hedging
Notional Value	$ 1,450,000,000		$ 1,450,000,000
Strike Rate (as a percent)	4.75%		4.75%
Fair Value	$ 0		$ 0
Interest Rate Swaps/Caps
Financial Instruments: Derivatives and Hedging
Amount of (Loss) Gain Recognized in Other Comprehensive Loss (Effective Portion)	(1,186,000)	(1,095,000)	(8,105,000)	(8,616,000)
Amount of Loss Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	4,468,000	2,737,000	6,631,000	5,484,000
Amount of (Loss) or Gain Recognized into Income (Ineffective Portion)	$ 1,000	$ (14,000)	$ (38,000)	$ (424,000)