Investments in Unconsolidated Joint Ventures (Details) (USD $)	3 Months Ended										12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Schedule of Equity Method Investments [Line Items]
Accumulated depreciation	$ (1,057,680,000)					$ (1,072,859,000)					$ (1,057,680,000)		$ (1,072,859,000)		$ (958,652,000)		$ (845,305,000)
Operating real estate	5,226,533,000					3,818,484,000					5,226,533,000		3,818,484,000
Development in Process	209,187,000					248,602,000					209,187,000		248,602,000
Land held for development	233,055,000					249,221,000					233,055,000		249,221,000
Other liabilities	250,819,000					185,956,000					250,819,000		185,956,000
Company's net investment in unconsolidated joint ventures	179,655,000					169,021,000					179,655,000		169,021,000
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	41,700,000					28,500,000					41,700,000		28,500,000
Total revenue	192,427,000		155,349,000	151,026,000	147,128,000	144,431,000		140,515,000	137,987,000	137,346,000
Operating income											203,047,000		189,942,000		190,995,000
Interest											(127,115,000)		(103,363,000)		(101,988,000)
Depreciation and amortization											(205,147,000)		(167,421,000)		(171,714,000)
Discontinued operations	51,832,000		6,544,000	13,633,000	49,830,000	16,795,000		7,539,000	12,956,000	13,714,000	121,839,000		51,004,000		106,065,000
Equity in earnings (loss) of unconsolidated joint ventures											6,067,000		(681,000)		3,496,000
Liberty Venture I, LP [Member]
Schedule of Equity Method Investments [Line Items]
Real estate assets	129,354,000					129,296,000					129,354,000		129,296,000
Accumulated depreciation	(32,617,000)					(28,849,000)					(32,617,000)		(28,849,000)
Operating real estate	96,737,000					100,447,000					96,737,000		100,447,000
Development in Process	2,226,000										2,226,000
Land held for development	2,842,000					2,760,000					2,842,000		2,760,000
Other assets	11,531,000					9,845,000					11,531,000		9,845,000
Total assets	113,336,000					113,052,000					113,336,000		113,052,000
Debt	72,121,000					73,426,000					72,121,000		73,426,000
Other liabilities	4,032,000					3,754,000					4,032,000		3,754,000
Equity	37,183,000					35,872,000					37,183,000		35,872,000
Total liabilities and equity	113,336,000					113,052,000					113,336,000		113,052,000
Company's net investment in unconsolidated joint ventures	8,551,000	[1]				8,205,000	[1]				8,551,000	[1]	8,205,000	[1]
Total revenue											16,238,000		15,328,000	[2]	17,008,000	[2]
Operating expense											5,248,000		5,277,000	[2]	5,912,000	[2]
Operating income											10,990,000		10,051,000	[2]	11,096,000	[2]
Interest											(5,318,000)		(5,402,000)	[2]	(5,472,000)	[2]
Depreciation and amortization											(4,414,000)		(3,930,000)	[2]	(4,088,000)	[2]
Other income/(expense)											53,000		40,000	[2]	985,000	[2]
Discontinued operations											0
Gain (Loss) on Sale of Investments													0	[2]	1,515,000	[2]
Net income (loss)											1,311,000		759,000		4,036,000
Equity in earnings (loss) of unconsolidated joint ventures											530,000		306,000		1,212,000
Kings Hill Unit Trust [Member]
Schedule of Equity Method Investments [Line Items]
Real estate assets	182,220,000					193,628,000					182,220,000		193,628,000
Accumulated depreciation	(25,006,000)					(22,666,000)					(25,006,000)		(22,666,000)
Operating real estate	157,214,000					170,962,000					157,214,000		170,962,000
Development in Process	0										0
Land held for development	0					0					0		0
Other assets	20,173,000					13,736,000					20,173,000		13,736,000
Total assets	177,387,000					184,698,000					177,387,000		184,698,000
Debt	97,091,000					117,308,000					97,091,000		117,308,000
Other liabilities	100,112,000					77,832,000					100,112,000		77,832,000
Equity	(19,816,000)					(10,442,000)					(19,816,000)		(10,442,000)
Total liabilities and equity	177,387,000					184,698,000					177,387,000		184,698,000
Company's net investment in unconsolidated joint ventures	12,772,000	[1]				10,341,000	[1]				12,772,000	[1]	10,341,000	[1]
Total revenue											12,701,000		15,642,000	[2]	16,389,000	[2]
Operating expense											4,187,000		4,237,000	[2]	3,372,000	[2]
Operating income											8,514,000		11,405,000	[2]	13,017,000	[2]
Interest											(5,133,000)		(6,520,000)	[2]	(5,979,000)	[2]
Depreciation and amortization											(3,829,000)		(3,731,000)	[2]	(4,219,000)	[2]
Other income/(expense)											71,000		(160,000)	[2]	(511,000)	[2]
Discontinued operations											(5,647,000)
Gain (Loss) on Sale of Investments													0	[2]	0	[2]
Net income (loss)											(6,024,000)		994,000		2,308,000
Equity in earnings (loss) of unconsolidated joint ventures											(908,000)		352,000		637,000
Liberty Illinois, LP [Member]
Schedule of Equity Method Investments [Line Items]
Real estate assets	261,375,000					259,786,000					261,375,000		259,786,000
Accumulated depreciation	(43,304,000)					(36,978,000)					(43,304,000)		(36,978,000)
Operating real estate	218,071,000					222,808,000					218,071,000		222,808,000
Development in Process	0										0
Land held for development	42,770,000					42,734,000					42,770,000		42,734,000
Other assets	20,346,000					14,974,000					20,346,000		14,974,000
Total assets	281,187,000					280,516,000					281,187,000		280,516,000
Debt	140,400,000					140,400,000					140,400,000		140,400,000
Other liabilities	7,936,000					7,675,000					7,936,000		7,675,000
Equity	132,851,000					132,441,000					132,851,000		132,441,000
Total liabilities and equity	281,187,000					280,516,000					281,187,000		280,516,000
Company's net investment in unconsolidated joint ventures	21,688,000	[1]				21,331,000	[1]				21,688,000	[1]	21,331,000	[1]
Total revenue											24,455,000		22,156,000	[2]	20,245,000	[2]
Operating expense											8,353,000		8,093,000	[2]	8,055,000	[2]
Operating income											16,102,000		14,063,000	[2]	12,190,000	[2]
Interest											(8,348,000)		(8,348,000)	[2]	(8,348,000)	[2]
Depreciation and amortization											(7,382,000)		(7,395,000)	[2]	(7,342,000)	[2]
Other income/(expense)											38,000		31,000	[2]	(56,000)	[2]
Discontinued operations											0
Gain (Loss) on Sale of Investments													0	[2]	0	[2]
Net income (loss)											410,000		(1,649,000)		(3,556,000)
Equity in earnings (loss) of unconsolidated joint ventures											618,000		106,000		(394,000)
Blythe Valley JV Sarl [Member]
Schedule of Equity Method Investments [Line Items]
Real estate assets						124,204,000							124,204,000
Accumulated depreciation						(23,764,000)							(23,764,000)
Operating real estate						100,440,000							100,440,000
Land held for development						38,683,000							38,683,000
Other assets						10,934,000							10,934,000
Total assets						150,057,000							150,057,000
Debt						192,803,000							192,803,000
Other liabilities						80,326,000							80,326,000
Equity						(123,072,000)							(123,072,000)
Total liabilities and equity						150,057,000							150,057,000
Company's net investment in unconsolidated joint ventures						0	[1]						0	[1]
Total revenue													14,278,000	[2]	13,950,000	[2]
Operating expense													3,921,000	[2]	3,942,000	[2]
Operating income													10,357,000	[2]	10,008,000	[2]
Interest													(12,130,000)	[2]	(14,991,000)	[2]
Depreciation and amortization													(4,148,000)	[2]	(4,951,000)	[2]
Other income/(expense)													211,000	[2]	(191,000)	[2]
Gain (Loss) on Sale of Investments													(77,026,000)	[2]	(1,605,000)	[2]
Net income (loss)													(82,736,000)		(11,730,000)
Equity in earnings (loss) of unconsolidated joint ventures													(5,610,000)		(1,898,000)
Liberty Washington, LP [Member]
Schedule of Equity Method Investments [Line Items]
Real estate assets	887,452,000					929,790,000					887,452,000		929,790,000
Accumulated depreciation	(131,064,000)					(116,072,000)					(131,064,000)		(116,072,000)
Operating real estate	756,388,000					813,718,000					756,388,000		813,718,000
Development in Process	0										0
Land held for development	2,000,000					2,000,000					2,000,000		2,000,000
Other assets	58,701,000					62,647,000					58,701,000		62,647,000
Total assets	817,089,000					878,365,000					817,089,000		878,365,000
Debt	319,856,000					341,804,000					319,856,000		341,804,000
Other liabilities	15,012,000					21,989,000					15,012,000		21,989,000
Equity	482,221,000					514,572,000					482,221,000		514,572,000
Total liabilities and equity	817,089,000					878,365,000					817,089,000		878,365,000
Company's net investment in unconsolidated joint ventures	72,981,000	[1]				76,965,000	[1]				72,981,000	[1]	76,965,000	[1]
Total revenue											75,821,000		81,128,000	[2]	76,811,000	[2]
Operating expense											27,549,000		27,901,000	[2]	27,074,000	[2]
Operating income											48,272,000		53,227,000	[2]	49,737,000	[2]
Interest											(18,946,000)		(21,260,000)	[2]	(22,998,000)	[2]
Depreciation and amortization											(28,392,000)		(28,749,000)	[2]	(28,618,000)	[2]
Other income/(expense)											122,000		149,000	[2]	125,000	[2]
Discontinued operations											(8,731,000)
Gain (Loss) on Sale of Investments													0	[2]	0	[2]
Net income (loss)											(7,675,000)		3,367,000		(1,754,000)
Equity in earnings (loss) of unconsolidated joint ventures											3,748,000		3,243,000		1,889,000
Liberty Commerz 1701 JFK Boulevard, LP [Member]
Schedule of Equity Method Investments [Line Items]
Real estate assets	494,150,000					494,045,000					494,150,000		494,045,000
Accumulated depreciation	(83,461,000)					(69,572,000)					(83,461,000)		(69,572,000)
Operating real estate	410,689,000					424,473,000					410,689,000		424,473,000
Development in Process	0										0
Land held for development	0					0					0		0
Other assets	50,680,000					50,638,000					50,680,000		50,638,000
Total assets	461,369,000					475,111,000					461,369,000		475,111,000
Debt	321,401,000					324,000,000					321,401,000		324,000,000
Other liabilities	9,544,000					9,257,000					9,544,000		9,257,000
Equity	130,424,000					141,854,000					130,424,000		141,854,000
Total liabilities and equity	461,369,000					475,111,000					461,369,000		475,111,000
Company's net investment in unconsolidated joint ventures	24,740,000	[1]				27,305,000	[1]				24,740,000	[1]	27,305,000	[1]
Total revenue											62,411,000		62,484,000	[2]	62,225,000	[2]
Operating expense											23,074,000		22,935,000	[2]	20,575,000	[2]
Operating income											39,337,000		39,549,000	[2]	41,650,000	[2]
Interest											(20,391,000)		(20,501,000)	[2]	(20,445,000)	[2]
Depreciation and amortization											(14,734,000)		(15,411,000)	[2]	(15,494,000)	[2]
Other income/(expense)											(233,000)		(80,000)	[2]	(2,046,000)	[2]
Discontinued operations											0
Gain (Loss) on Sale of Investments													0	[2]	0	[2]
Net income (loss)											3,979,000		3,557,000		3,665,000
Equity in earnings (loss) of unconsolidated joint ventures											1,406,000		1,304,000		1,314,000
Other Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Real estate assets	70,274,000					69,680,000					70,274,000		69,680,000
Accumulated depreciation	(8,456,000)					(6,853,000)					(8,456,000)		(6,853,000)
Operating real estate	61,818,000					62,827,000					61,818,000		62,827,000
Development in Process	0										0
Land held for development	47,549,000					23,193,000					47,549,000		23,193,000
Other assets	15,911,000					14,294,000					15,911,000		14,294,000
Total assets	125,278,000					100,314,000					125,278,000		100,314,000
Debt	43,151,000					43,946,000					43,151,000		43,946,000
Other liabilities	9,846,000					6,173,000					9,846,000		6,173,000
Equity	72,281,000					50,195,000					72,281,000		50,195,000
Total liabilities and equity	125,278,000					100,314,000					125,278,000		100,314,000
Company's net investment in unconsolidated joint ventures	38,923,000	[1]				24,874,000	[1]				38,923,000	[1]	24,874,000	[1]
Total revenue											8,415,000		7,481,000	[2]	7,212,000	[2]
Operating expense											2,636,000		2,392,000	[2]	1,869,000	[2]
Operating income											5,779,000		5,089,000	[2]	5,343,000	[2]
Interest											(2,933,000)		(2,989,000)	[2]	(3,169,000)	[2]
Depreciation and amortization											(1,870,000)		(1,885,000)	[2]	(1,793,000)	[2]
Other income/(expense)											(37,000)		21,000	[2]	(509,000)	[2]
Discontinued operations											0
Gain (Loss) on Sale of Investments													0	[2]	1,253,000	[2]
Net income (loss)											939,000		236,000		1,125,000
Equity in earnings (loss) of unconsolidated joint ventures											673,000		(382,000)		736,000
Equity Method Investee [Member]
Schedule of Equity Method Investments [Line Items]
Real estate assets	2,024,825,000					2,200,429,000					2,024,825,000		2,200,429,000
Accumulated depreciation	(323,908,000)					(304,754,000)					(323,908,000)		(304,754,000)
Operating real estate	1,700,917,000					1,895,675,000					1,700,917,000		1,895,675,000
Development in Process	2,226,000										2,226,000
Land held for development	95,161,000					109,370,000					95,161,000		109,370,000
Other assets	177,342,000					177,068,000					177,342,000		177,068,000
Total assets	1,975,646,000					2,182,113,000					1,975,646,000		2,182,113,000
Debt	994,020,000					1,233,687,000					994,020,000		1,233,687,000
Other liabilities	146,482,000					207,006,000					146,482,000		207,006,000
Equity	835,144,000					741,420,000					835,144,000		741,420,000
Total liabilities and equity	1,975,646,000					2,182,113,000					1,975,646,000		2,182,113,000
Company's net investment in unconsolidated joint ventures	179,655,000	[1]				169,021,000	[1]				179,655,000	[1]	169,021,000	[1]
Total revenue											200,041,000		218,497,000	[2]	213,840,000	[2]
Operating expense											71,047,000		74,756,000	[2]	70,799,000	[2]
Operating income											128,994,000		143,741,000	[2]	143,041,000	[2]
Interest											(61,069,000)		(77,150,000)	[2]	(81,402,000)	[2]
Depreciation and amortization											(60,621,000)		(65,249,000)	[2]	(66,505,000)	[2]
Other income/(expense)											14,000		212,000	[2]	(2,203,000)	[2]
Discontinued operations											(14,378,000)
Gain (Loss) on Sale of Investments													(77,026,000)	[2]	1,163,000	[2]
Net income (loss)											(7,060,000)		(75,472,000)		(5,906,000)
Equity in earnings (loss) of unconsolidated joint ventures											$ 6,067,000		$ (681,000)		$ 3,496,000

[1] Differences between the Company's net investment in unconsolidated joint ventures and its underlying equity in the net assets of the venture are primarily a result of impairments related to the Company's investment in unconsolidated joint ventures, the deferral of gains associated with the sales of properties to joint ventures in which the Company retains an ownership interest and loans made to the joint ventures by the Company. These adjustments have resulted in an aggregate difference reducing the Company's investments in unconsolidated joint ventures by $41.7 million and $28.5 million as of December 31, 2013 and 2012, respectively. Differences between historical cost basis and the basis reflected at the joint venture level (other than loans) are typically depreciated over the life of the related asset.

[2] The years ended December 31, 2012 and 2011 have not been restated for discontinued operations.