Financial Instruments: Derivatives and Hedging (Details) (USD $)	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2010	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Financial Instruments: Derivatives and Hedging
Loss from settlement of hedges included in accumulated other comprehensive loss		$ 17,300,000		$ 17,300,000
Share of joint venture accumulated other comprehensive loss		18,300,000		18,300,000
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		35,500,000		35,500,000		35,400,000
Estimated current balance held in accumulated other comprehensive loss to be reclassified into earnings within the next 12 months		1,900,000
Amount of (Loss) or Gain Recognized in Other Comprehensive Loss (Effective Portion) on derivatives qualifying as hedges		(3,433,000)	(7,188,000)	(10,356,000)	(13,260,000)
Amount of (Loss) or Gain Reclassified from Accumulated Other Comprehensive Loss into Interest Expense/ Equity in net income of unconsolidated joint ventures (Effective Portion) on derivatives qualifying as hedges		(3,249,000)	(3,179,000)	(9,665,000)	(9,394,000)
Amount of (Loss) or Gain Recognized in Interest Expense/Equity in Net Income of Unconsolidated Joint Ventures (Ineffective Portion) on derivatives not qualifying as hedges		(666,000)	(493,000)	(997,000)	(168,000)
Amount of (Loss) or Gain Recognized in Interest Expense/Equity in Net Income of Unconsolidated Joint Ventures (Ineffective Portion) on derivatives qualifying as hedges		(1,000)	(1,000)	(2,000)	(17,000)
Interest Rate Cap expiring in April, 2013
Financial Instruments: Derivatives and Hedging
Notional Value		775,000,000		775,000,000
Strike Rate (as a percent)		3.65%		3.65%
Interest Rate Cap
Financial Instruments: Derivatives and Hedging
Notional Value		280,000,000		280,000,000
Strike Rate (as a percent)		6.00%		6.00%
Interest Rate Swap
Financial Instruments: Derivatives and Hedging
Notional Value		30,000,000		30,000,000
Strike Rate (as a percent)		2.295%		2.295%
Interest Rate Cap 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%
Currency Hedge
Financial Instruments: Derivatives and Hedging
Notional Value		20,748,000		20,748,000
Strike Rate		1.55185		1.55185
Level 2
Financial Instruments: Derivatives and Hedging
Fair Value		2,200,000		2,200,000
Level 2 | Interest Rate Swap
Financial Instruments: Derivatives and Hedging
Fair Value		(2,034,000)		(2,034,000)
Level 2 | Interest Rate Cap expiring in February, 2015
Financial Instruments: Derivatives and Hedging
Fair Value		(86,000)		(86,000)
Level 2 | Currency Hedge
Financial Instruments: Derivatives and Hedging
Fair Value		$ (122,000)		$ (122,000)