Segment Information (Summary of net income and EBITDA reconciliation by segment) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Segment Information
Total revenues	$ 620,848	$ 613,037
Total expenses	464,381	613,317
Operating income (loss)	156,467	(280)
Income (loss) from partially owned entities	1,445	(4,240)
Income from real estate fund investments	268	11,284
Interest and other investment income, net	9,228	3,518
Interest and debt expense	(94,285)	(100,489)
Net gains on sale of residential condominiums	501	714
Income (loss) before income taxes	73,624	(89,493)
Income tax expense	(2,205)	(2,831)
Income (loss) from continuing operations	71,419	(92,324)
Income from discontinued operations	2,428	716
Net income (loss)	73,847	(91,608)
Less net income attributable to noncontrolling interests in consolidated subsidiaries	(6,737)	(9,678)
Net income (loss) attributable to the Operating Partnership	67,110	(101,286)
Interest and debt expense (2)	116,327	126,120
Depreciation and amortization (2)	171,537	174,811
Income tax expense	2,429	3,261
EBITDA	357,403	202,906
Operating Segments | New York
Segment Information
Total revenues	426,239	410,825
Total expenses	280,821	269,595
Operating income (loss)	145,418	141,230
Income (loss) from partially owned entities	(2,093)	(3,563)
Income from real estate fund investments	0	0
Interest and other investment income, net	1,472	1,115
Interest and debt expense	(57,987)	(54,586)
Net gains on sale of residential condominiums	0	0
Income (loss) before income taxes	86,810	84,196
Income tax expense	(143)	(959)
Income (loss) from continuing operations	86,667	83,237
Income from discontinued operations	0	0
Net income (loss)	86,667	83,237
Less net income attributable to noncontrolling interests in consolidated subsidiaries	(2,844)	(3,429)
Net income (loss) attributable to the Operating Partnership	83,823	79,808
Interest and debt expense (2)	75,923	71,198
Depreciation and amortization (2)	112,810	108,403
Income tax expense	227	1,090
EBITDA	272,783	260,499
Operating Segments | Washington DC
Segment Information
Total revenues	116,207	128,012
Total expenses	83,988	256,565
Operating income (loss)	32,219	(128,553)
Income (loss) from partially owned entities	32	(2,265)
Income from real estate fund investments	0	0
Interest and other investment income, net	64	58
Interest and debt expense	(11,561)	(15,935)
Net gains on sale of residential condominiums	0	0
Income (loss) before income taxes	20,754	(146,695)
Income tax expense	(354)	(264)
Income (loss) from continuing operations	20,400	(146,959)
Income from discontinued operations	0	0
Net income (loss)	20,400	(146,959)
Less net income attributable to noncontrolling interests in consolidated subsidiaries	0	0
Net income (loss) attributable to the Operating Partnership	20,400	(146,959)
Interest and debt expense (2)	13,499	18,996
Depreciation and amortization (2)	36,383	42,230
Income tax expense	367	265
EBITDA	70,649	(85,468)
Operating Segments | Other
Segment Information
Total revenues	78,402	74,200
Total expenses	99,572	87,157
Operating income (loss)	(21,170)	(12,957)
Income (loss) from partially owned entities	3,506	1,588
Income from real estate fund investments	268	11,284
Interest and other investment income, net	7,692	2,345
Interest and debt expense	(24,737)	(29,968)
Net gains on sale of residential condominiums	501	714
Income (loss) before income taxes	(33,940)	(26,994)
Income tax expense	(1,708)	(1,608)
Income (loss) from continuing operations	(35,648)	(28,602)
Income from discontinued operations	2,428	716
Net income (loss)	(33,220)	(27,886)
Less net income attributable to noncontrolling interests in consolidated subsidiaries	(3,893)	(6,249)
Net income (loss) attributable to the Operating Partnership	(37,113)	(34,135)
Interest and debt expense (2)	26,905	35,926
Depreciation and amortization (2)	22,344	24,178
Income tax expense	1,835	1,906
EBITDA	$ 13,971	$ 27,875