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	Mar. 31, 2010	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		15,900,000			15,900,000
Share of joint venture accumulated other comprehensive loss		5,900,000			5,900,000
Net loss on forward swaps	19,500,000
Amortization period of the loss from the settlement of the hedges				10 years
Accumulated Other Comprehensive Loss relating to derivatives, including share of joint venture		21,800,000			21,800,000		32,900,000
Estimated current balance held in accumulated other comprehensive loss to be reclassified into earnings within the next 12 months					2,300,000
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) or Recognized in Interest Expense/Equity in Net Income 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)
Share of joint venture of accumulated other comprehensive loss reclassified into equity in net income from unconsolidated joint ventures within the next 12 months					4,900,000
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%
Interest Rate Cap 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%
Level 2 | Interest Rate Cap 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)