Investments in Unconsolidated Joint Ventures (Statements of Operations of the Joint Ventures) (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Total revenue		$ 636,061	$ 625,228	$ 623,546	$ 665,985	$ 624,240	$ 629,884	$ 618,221	$ 618,476	$ 2,550,820		$ 2,490,821		$ 2,396,998
Expenses
Depreciation and amortization										694,403		639,542		628,573
Total expenses										1,725,036		1,641,456		1,595,176
Operating income										825,784		849,365		801,822
Other income (expense)
Interest expense										(412,849)		(432,196)		(455,743)
Net income										569,977		799,918		526,057
Income from unconsolidated joint ventures										8,074		22,770		12,769
Gain on sale of investment in unconsolidated joint venture										59,370		0		0
Straight-line rent adjustments										31,700		80,000		63,100
Mortgage and notes payable, net		2,063,087				3,435,242				2,063,087		3,435,242
Above and below market rent adjustments, net										30,200		35,900		48,300
Gain on sale of investment in unconsolidated joint venture										55,707		0		0
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Total revenue	[1]									177,182		155,642		158,161
Expenses
Operating										76,741		65,093		62,974
Depreciation and amortization										44,989		36,057		37,041
Total expenses										121,730		101,150		100,015
Operating income										55,452		54,492		58,146
Other income (expense)
Interest expense										(34,016)		(32,176)		(31,896)
Net income										21,436		22,316		26,250
Company's share of net income										9,873		22,031	[2]	11,913
Basis differential										(1,799)	[3]	739		856
Income from unconsolidated joint ventures										8,074		22,770		12,769
Straight-line rent adjustments										18,100		3,900		$ 3,000
Mortgage and notes payable, net		$ 865,665				830,125				865,665		830,125
BP/CRF 901 New York Avenue LLC [Member]
Other income (expense)
Mortgage and notes payable, net						$ 225,000						225,000
Gain on sale of investment in unconsolidated joint venture												$ 24,500
Colorado Center [Member]
Other income (expense)
Straight-line rent adjustments										1,400
Above and below market rent adjustments, net										$ (900)

[1] Includes straight-line rent adjustments of approximately $18.1 million, $3.9 million and $3.0 million for the years ended December 31, 2016, 2015 and 2014, respectively.

[2] During the year ended December 31, 2015, the Company received a distribution of approximately $24.5 million, which was generated from the excess loan proceeds from the refinancing of 901 New York Avenue’s mortgage loan to a new 10-year mortgage loan totaling $225.0 million. The Company’s allocation of income and distributions for the year ended December 31, 2015 was not proportionate to its nominal ownership interest as a result of the achievement of specified investment return thresholds, as provided for in the joint venture agreement.

[3] Includes the Company’s share of straight-line rent adjustments of approximately $1.4 million and net below-market rent adjustments of approximately $0.9 million for the year ended December 31, 2016.