Real Estate Fund Investments - Schedule of Amounts Recognized in Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Schedule Of Balance Sheet And Income Statement Items [Line Items]
Rental income	$ 145,917		$ 289,160
Tenant reimbursement income	12,063		25,551
Fee and other income	4,948		9,443
Total revenues	162,928		324,154
Operating	57,781		119,665
Depreciation and amortization	79,421		153,004
General and administrative	9,133		21,746
Total expenses	154,543		303,762
Operating income (loss)	8,385		20,392
Unrealized gains on interest rate swaps	21,747		33,725
Interest and debt expense	(42,236)		(84,124)
Net income (loss) before income taxes	4,491		(6,362)
Income tax benefit (expense)	(1,343)		(1,917)
Net income (loss)	$ 3,148		$ (8,279)
1633 Broadway [Member]
Schedule Of Balance Sheet And Income Statement Items [Line Items]
Rental income		$ 37,251		$ 72,970
Tenant reimbursement income		3,096		5,913
Fee and other income		702		1,224
Total revenues		41,049		80,107
Building operating		13,268		26,879
Related party management fees		784		1,485
Operating		14,052		28,364
Depreciation and amortization		2,780		5,567
General and administrative		10		10
Total expenses		16,842		33,941
Operating income (loss)		24,207		46,166
Unrealized gains on interest rate swaps		5,665		12,945
Interest and debt expense		(12,894)		(25,625)
Net income (loss) before income taxes		16,978		33,486
Net income (loss)		16,978		33,486
900 Third Avenue [Member]
Schedule Of Balance Sheet And Income Statement Items [Line Items]
Rental income		8,982		17,764
Tenant reimbursement income		751		1,514
Fee and other income		168		612
Total revenues		9,901		19,890
Building operating		4,038		8,083
Related party management fees		261		525
Operating		4,299		8,608
Depreciation and amortization		2,144		3,731
General and administrative		24		31
Total expenses		6,467		12,370
Operating income (loss)		3,434		7,520
Unrealized gains on interest rate swaps		1,169		2,935
Interest and debt expense		(3,696)		(7,353)
Net income (loss) before income taxes		907		3,102
Net income (loss)		907		3,102
31 West 52nd Street [Member]
Schedule Of Balance Sheet And Income Statement Items [Line Items]
Rental income		18,122		36,221
Tenant reimbursement income		1,300		2,489
Fee and other income		1,333		2,615
Total revenues		20,755		41,325
Building operating		5,774		11,517
Related party management fees		329		655
Operating		6,103		12,172
Depreciation and amortization		5,545		11,074
General and administrative		7		34
Total expenses		11,655		23,280
Operating income (loss)		9,100		18,045
Unrealized gains on interest rate swaps		1,686		4,288
Interest and debt expense		(5,564)		(11,069)
Net income (loss) before income taxes		5,222		11,264
Net income (loss)		5,222		11,264
1301 Avenue of the Americas [Member]
Schedule Of Balance Sheet And Income Statement Items [Line Items]
Rental income		27,139		53,749
Tenant reimbursement income		2,318		4,434
Fee and other income		1,087		1,657
Total revenues		30,544		59,840
Building operating		13,008		25,688
Related party management fees		427		837
Operating		13,435		26,525
Depreciation and amortization		9,341		18,555
General and administrative		24		51
Total expenses		22,800		45,131
Operating income (loss)		7,744		14,709
Unrealized gains on interest rate swaps		2,872		6,125
Interest and debt expense		(15,379)		(30,549)
Net income (loss) before income taxes		(4,763)		(9,715)
Net income (loss)		(4,763)		(9,715)
One Market Plaza [Member]
Schedule Of Balance Sheet And Income Statement Items [Line Items]
Rental income		17,910		36,123
Tenant reimbursement income		273		661
Fee and other income		681		2,044
Total revenues		18,864		38,828
Building operating		6,836		14,001
Related party management fees		177		394
Operating		7,013		14,395
Depreciation and amortization		8,682		17,686
General and administrative		281		294
Total expenses		15,976		32,375
Operating income (loss)		2,888		6,453
Unrealized gains on interest rate swaps		3,529		10,444
Interest and debt expense		(13,334)		(27,072)
Net income (loss) before income taxes		(6,917)		(10,175)
Net income (loss)		(6,917)		(10,175)
Liberty Place [Member]
Schedule Of Balance Sheet And Income Statement Items [Line Items]
Rental income		1,690		3,729
Tenant reimbursement income		563		1,184
Fee and other income		9		23
Total revenues		2,262		4,936
Building operating		1,086		2,168
Related party management fees		61		132
Operating		1,147		2,300
General and administrative		11		16
Total expenses		1,158		2,316
Operating income (loss)		1,104		2,620
Interest and debt expense		(945)		(1,890)
Unrealized depreciation on investment in real estate		(459)		(489)
Net income (loss) before income taxes		(300)		241
Income tax benefit (expense)		(29)		(26)
Net income (loss)		(329)		215
1899 Pennsylvania Avenue [Member]
Schedule Of Balance Sheet And Income Statement Items [Line Items]
Rental income		1,940		4,044
Tenant reimbursement income		967		2,107
Fee and other income		28		56
Total revenues		2,935		6,207
Building operating		1,348		2,605
Related party management fees		66		141
Operating		1,414		2,746
Depreciation and amortization		940		1,923
General and administrative		11		16
Total expenses		2,365		4,685
Operating income (loss)		570		1,522
Interest and debt expense		(1,129)		(2,257)
Net income (loss) before income taxes		(559)		(735)
Income tax benefit (expense)		114		182
Net income (loss)		(445)		(553)
2099 Pennsylvania Avenue [Member]
Schedule Of Balance Sheet And Income Statement Items [Line Items]
Rental income		43		76
Tenant reimbursement income		1		3
Fee and other income		7		10
Total revenues		51		89
Building operating		1,143		2,223
Related party management fees		1		2
Operating		1,144		2,225
General and administrative		12		399
Total expenses		1,156		2,624
Operating income (loss)		(1,105)		(2,535)
Interest and debt expense		(1,380)		(2,208)
Unrealized depreciation on investment in real estate		(520)		(530)
Net income (loss) before income taxes		(3,005)		(5,273)
Net income (loss)		(3,005)		(5,273)
425 Eye Street [Member]
Schedule Of Balance Sheet And Income Statement Items [Line Items]
Rental income		2,642		5,300
Tenant reimbursement income		83		827
Fee and other income		(179)
Total revenues		2,546		6,127
Building operating		1,390		2,904
Related party management fees		79		184
Operating		1,469		3,088
Depreciation and amortization		1,398		2,793
General and administrative		107		114
Total expenses		2,974		5,995
Operating income (loss)		(428)		132
Interest and debt expense		(1,301)		(2,520)
Net income (loss) before income taxes		(1,729)		(2,388)
Income tax benefit (expense)		24		(2,315)
Net income (loss)		$ (1,705)		$ (4,703)