Investments in Unconsolidated Joint Ventures (Statements of Operations of the Joint Ventures) (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Mortgage notes payable		$ 3,438,714				$ 4,309,484				$ 3,438,714		$ 4,309,484
Total revenue		624,240	$ 629,884	$ 618,221	$ 618,476	613,707	$ 618,803	$ 589,794	$ 574,694	2,490,821		2,396,998	$ 2,135,539
Expenses
Depreciation and amortization										639,542		628,573	560,637
Total expenses										1,641,456		1,595,176	1,457,419
Operating income										849,365		801,822	678,120
Other income (expense)
Interest expense										(432,196)		(455,743)	(446,880)
(Losses) gains from early extinguishments of debt										(22,040)		(10,633)	122
Income (loss) from continuing operations		85,406	$ 123,792	$ 100,739	$ 114,086	85,323	$ 109,038	$ 95,901	$ 67,756	424,023		358,018	703,648
Net income (loss)										799,918		526,057	841,440
Income from unconsolidated joint ventures										22,770		12,769	75,074
Straight-line rent adjustments										80,000		63,100	65,800
Above and below market rent adjustments, net										35,900		48,300	28,000
Proceeds from Sale of Equity Method Investments										24,527		1,491	225,862
Gain on consolidation of joint ventures										0		0	385,991
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Mortgage notes payable		833,895				$ 830,075				833,895		830,075
Total revenue	[1]									155,642		158,161	311,548
Expenses
Operating										65,093		62,974	105,319
Depreciation and amortization										36,057		37,041	86,088
Total expenses										101,150		100,015	191,407
Operating income										54,492		58,146	120,141
Other income (expense)
Interest expense										(32,176)		(31,896)	(112,535)
(Losses) gains from early extinguishments of debt										0		0	(1,677)
Income (loss) from continuing operations										22,316		26,250	5,929
Gains on sale of real estate										0		0	14,207
Net income (loss)										22,316		26,250	20,136
Company's share of net income (loss)										22,031	[2]	11,913	4,612
Gains on sale of real estate										0		0	54,501
Basis differential										739		856	(1,017)
Elimination of inter-entity interest on partner loan										0		0	16,978
Income from unconsolidated joint ventures										22,770		12,769	75,074
Straight-line rent adjustments										3,900		3,000	7,800
Above and below market rent adjustments, net										(200)		(100)	33,700
Gain on consolidation of joint ventures										0		$ 0	$ 385,991
BP/CRF 901 New York Avenue LLC [Member]
Schedule of Equity Method Investments [Line Items]
Mortgage notes payable		$ 225,000								225,000
Other income (expense)
Proceeds from Sale of Equity Method Investments										$ 24,500

[1] Includes straight-line rent adjustments of $3.9 million, $3.0 million and $7.8 million for the years ended December 31, 2015, 2014 and 2013, respectively. Includes net above-/below-market rent adjustments of $(0.2) million, $(0.1) million and $33.7 million for the years ended December 31, 2015, 2014 and 2013, 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.