Fair Value of Assets and Liabilities (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Nonrecurring Fair Value Measurements:
Properties held and used	$ 4,938,862,000		$ 4,938,862,000		$ 4,642,106,000
Effects of interest rate derivatives on our consolidated statements of operations and consolidated statements of comprehensive income (loss)
Unrealized gain on derivative instruments	627,000	2,782,000	1,627,000	3,833,000
CBD Office
Nonrecurring Fair Value Measurements:
Loss on asset impairment			22,700,000
Interest Rate Swap
Recurring Fair Value Measurements:
Interest rate swap agreements qualifying as cash flow hedges used for hedging mortgage note payable	172,400,000		172,400,000
Derivative, variable rate basis			LIBOR
Interest Rate Swap | Cash Flow Hedges
Recurring Fair Value Measurements:
Effective portion of interest rate swap contracts	(10,079,000)	(12,791,000)	(10,079,000)	(12,791,000)
Nonrecurring Fair Value Measurements:
Increase (Decrease) in fair value of interest rate cash flow hedges	600,000	2,800,000	1,600,000	3,800,000
Effects of interest rate derivatives on our consolidated statements of operations and consolidated statements of comprehensive income (loss)
Balance at beginning of period	(10,706,000)	(15,573,000)	(11,706,000)	(16,624,000)
Amount of income (loss) recognized in cumulative other comprehensive (loss) income	(632,000)	1,546,000	(861,000)	1,361,000
Amount of loss reclassified from cumulative other comprehensive (loss) income into interest expense	1,259,000	1,236,000	2,488,000	2,472,000
Unrealized gain on derivative instruments	627,000	2,782,000	1,627,000	3,833,000
Balance at end of period	(10,079,000)	(12,791,000)	(10,079,000)	(12,791,000)
Reclassification from cumulative other comprehensive income (loss) into interest expense, over the next 12 months	4,900,000		4,900,000
Recurring | Total Fair value
Recurring Fair Value Measurements:
Effective portion of interest rate swap contracts	(10,079,000)		(10,079,000)
Effects of interest rate derivatives on our consolidated statements of operations and consolidated statements of comprehensive income (loss)
Balance at end of period	(10,079,000)		(10,079,000)
Recurring | Fair Value at Reporting Date Using Significant Other Observable Inputs (Level 2)
Recurring Fair Value Measurements:
Effective portion of interest rate swap contracts	(10,079,000)		(10,079,000)
Effects of interest rate derivatives on our consolidated statements of operations and consolidated statements of comprehensive income (loss)
Balance at end of period	(10,079,000)		(10,079,000)
Nonrecurring | Carrying Amount | CBD Office
Nonrecurring Fair Value Measurements:
Properties held and used	42,300,000		42,300,000
Nonrecurring | Total Fair value
Nonrecurring Fair Value Measurements:
Properties held and used	19,589,000		19,589,000
Nonrecurring | Total Fair value | CBD Office
Nonrecurring Fair Value Measurements:
Properties held and used	19,600,000		19,600,000
Nonrecurring | Fair Value at Reporting Date Using Significant Unobservable Inputs (Level 3)
Nonrecurring Fair Value Measurements:
Properties held and used	$ 19,589,000		$ 19,589,000