Financial Instruments: Derivatives and Hedging (Details) (USD $)	1 Months Ended	3 Months Ended		6 Months Ended
	Mar. 31, 2010	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Financial Instruments: Derivatives and Hedging
Fair Value		$ 1,500,000		$ 1,500,000
Loss from settlement of hedges included in accumulated other comprehensive loss		16,400,000		16,400,000
Share of joint venture accumulated other comprehensive loss		6,000,000		6,000,000
Net loss on forward swaps	19,500,000
Amortization period of the loss from the settlement of hedges	10 years
Accumulated other comprehensive loss relating to derivatives		22,400,000		22,400,000		34,100,000
Estimated current balance held in accumulated other comprehensive loss to be reclassified into interest within the next 12 months				2,300,000
Estimated amount of amount of Loss reclassified from accumulated other comprehensive loss into equity in net income from unconsolidated joint ventures within the next 12 months.		4,900,000		4,900,000
Amount of Gain or (Loss) Recognized in Other Comprehensive Loss (Effective Portion) on derivatives qualifying as hedges		8,069,000	(6,865,000)	8,249,000	(6,953,000)
Amount of Loss Reclassified from Accumulated Other Comprehensive Loss into Interest Expense/ Equity in net income of unconsolidated joint ventures (Effective Portion) on derivatives qualifying as hedges		1,730,000	3,217,000	3,438,000	6,420,000
Amount of Gain or (Loss) Recognized in Interest Expense/Equity in Net Income (Loss)of Unconsolidated Joint Ventures (Ineffective Portion) on derivatives qualifying as hedges		5,000	1,000	5,000	1,000
Amount of Gain or (Loss) Recognized in Interest Expense/Equity in Net Income of Unconsolidated Joint Ventures (Ineffective Portion) on derivatives not qualifying as hedges		4,000	380,000	(11,000)	(331,000)
Interest Rate Swap Expiring in June 2016
Financial Instruments: Derivatives and Hedging
Notional Value		30,000,000		30,000,000
Strike Rate (as a percent)		2.295%		2.295%
Interest Rate Swap expiring in February, 2015
Financial Instruments: Derivatives and Hedging
Notional Value		8,500,000		8,500,000
Strike Rate (as a percent)		0.74%		0.74%
Interest Rate Cap expiring in November, 2013
Financial Instruments: Derivatives and Hedging
Notional Value		271,912,000		271,912,000
Strike Rate (as a percent)		6.00%		6.00%
Level 2 | Interest Rate Swap Expiring in June 2016
Financial Instruments: Derivatives and Hedging
Fair Value		(1,426,000)		(1,426,000)
Level 2 | Interest Rate Swap expiring in February, 2015
Financial Instruments: Derivatives and Hedging
Fair Value		$ (54,000)		$ (54,000)