Schedule III - Real Estate and Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
Real Estate And Accumulated Depreciation [Line Items]
Encumbrances				$ 3,583,100
Initial cost to company, Land				2,209,506
Initial cost to company, Building and Improvements				5,823,744
Costs capitalized subsequent to acquisition, Building and Improvements				296,225
Gross amount at which carried at close of period, Land				2,209,506
Gross amount at which carried at close of period, Buildings and Improvements				6,119,969
Gross amount at which carried at close of period, Total	$ 8,329,475	$ 7,849,093	$ 7,652,117	8,329,475
Accumulated depreciation and amortization	(487,945)	(318,161)	(243,089)	(487,945)
Costs capitalized subsequent to acquisition, Building and Improvements, other				3,528
Gross amount at which carried at close of period, Buildings and Improvements, other				3,528
Gross amount at which carried at close of period, other				3,528
Accumulated depreciation and amortization, other	$ (719)
Date acquired, other	Nov. 24, 2014
Real Estate:
Beginning balance	$ 7,849,093	7,652,117	7,530,239
Acquisitions	484,916	504,684
Buildings and improvements	82,862	116,038	123,277
Assets held for sale		(412,315)
Assets sold and written-off	(87,396)	(11,431)	(1,399)
Ending balance	8,329,475	7,849,093	7,652,117
Accumulated Depreciation:
Beginning balance	318,161	243,089	81,050
Additions charged to expense	182,732	168,847	163,438
Assets held for sale		(82,344)
Accumulated depreciation related to assets sold and written-off	(12,948)	(11,431)	(1,399)
Ending balance	$ 487,945	$ 318,161	$ 243,089
Minimum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed, other	5 years
Maximum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed, other	40 years
1633 Broadway [Member]
Real Estate And Accumulated Depreciation [Line Items]
Encumbrances				1,030,100
Initial cost to company, Land				502,846
Initial cost to company, Building and Improvements				1,398,341
Costs capitalized subsequent to acquisition, Building and Improvements				74,427
Gross amount at which carried at close of period, Land				502,846
Gross amount at which carried at close of period, Buildings and Improvements				1,472,768
Gross amount at which carried at close of period, Total	$ 1,975,614			1,975,614
Accumulated depreciation and amortization	$ (123,730)			(123,730)
Date of construction	Dec. 31, 1971
Date acquired	Nov. 24, 2014
Real Estate:
Ending balance	$ 1,975,614
Accumulated Depreciation:
Ending balance	$ 123,730
1633 Broadway [Member] | Minimum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	5 years
1633 Broadway [Member] | Maximum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	40 years
1301 Avenue of Americas [Member]
Real Estate And Accumulated Depreciation [Line Items]
Encumbrances				850,000
Initial cost to company, Land				406,039
Initial cost to company, Building and Improvements				1,051,697
Costs capitalized subsequent to acquisition, Building and Improvements				74,934
Gross amount at which carried at close of period, Land				406,039
Gross amount at which carried at close of period, Buildings and Improvements				1,126,631
Gross amount at which carried at close of period, Total	$ 1,532,670			1,532,670
Accumulated depreciation and amortization	$ (93,817)			(93,817)
Date of construction	Dec. 31, 1963
Date acquired	Nov. 24, 2014
Real Estate:
Ending balance	$ 1,532,670
Accumulated Depreciation:
Ending balance	$ 93,817
1301 Avenue of Americas [Member] | Minimum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	5 years
1301 Avenue of Americas [Member] | Maximum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	40 years
31 West 52nd Street [Member]
Real Estate And Accumulated Depreciation [Line Items]
Encumbrances				500,000
Initial cost to company, Land				221,318
Initial cost to company, Building and Improvements				604,994
Costs capitalized subsequent to acquisition, Building and Improvements				8,529
Gross amount at which carried at close of period, Land				221,318
Gross amount at which carried at close of period, Buildings and Improvements				613,523
Gross amount at which carried at close of period, Total	$ 834,841			834,841
Accumulated depreciation and amortization	$ (51,908)			(51,908)
Date of construction	Dec. 31, 1987
Date acquired	Nov. 24, 2014
Real Estate:
Ending balance	$ 834,841
Accumulated Depreciation:
Ending balance	$ 51,908
31 West 52nd Street [Member] | Minimum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	5 years
31 West 52nd Street [Member] | Maximum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	40 years
1325 Avenue of the Americas [Member]
Real Estate And Accumulated Depreciation [Line Items]
Initial cost to company, Land				174,688
Initial cost to company, Building and Improvements				370,553
Costs capitalized subsequent to acquisition, Building and Improvements				18,494
Gross amount at which carried at close of period, Land				174,688
Gross amount at which carried at close of period, Buildings and Improvements				389,047
Gross amount at which carried at close of period, Total	$ 563,735			563,735
Accumulated depreciation and amortization	$ (33,663)			(33,663)
Date of construction	Dec. 31, 1989
Date acquired	Nov. 24, 2014
Real Estate:
Ending balance	$ 563,735
Accumulated Depreciation:
Ending balance	$ 33,663
1325 Avenue of the Americas [Member] | Minimum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	5 years
1325 Avenue of the Americas [Member] | Maximum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	40 years
900 Third Avenue [Member]
Real Estate And Accumulated Depreciation [Line Items]
Initial cost to company, Land				103,741
Initial cost to company, Building and Improvements				296,031
Costs capitalized subsequent to acquisition, Building and Improvements				11,905
Gross amount at which carried at close of period, Land				103,741
Gross amount at which carried at close of period, Buildings and Improvements				307,936
Gross amount at which carried at close of period, Total	$ 411,677			411,677
Accumulated depreciation and amortization	$ (29,407)			(29,407)
Date of construction	Dec. 31, 1983
Date acquired	Nov. 24, 2014
Real Estate:
Ending balance	$ 411,677
Accumulated Depreciation:
Ending balance	$ 29,407
900 Third Avenue [Member] | Minimum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	5 years
900 Third Avenue [Member] | Maximum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	40 years
Total New York
Real Estate And Accumulated Depreciation [Line Items]
Encumbrances				2,380,100
Initial cost to company, Land				1,408,632
Initial cost to company, Building and Improvements				3,721,616
Costs capitalized subsequent to acquisition, Building and Improvements				188,289
Gross amount at which carried at close of period, Land				1,408,632
Gross amount at which carried at close of period, Buildings and Improvements				3,909,905
Gross amount at which carried at close of period, Total	$ 5,318,537			5,318,537
Accumulated depreciation and amortization	(332,525)			(332,525)
Real Estate:
Ending balance	5,318,537
Accumulated Depreciation:
Ending balance	332,525
425 Eye Street [Member]
Real Estate And Accumulated Depreciation [Line Items]
Initial cost to company, Land				93,669
Initial cost to company, Building and Improvements				98,088
Costs capitalized subsequent to acquisition, Building and Improvements				5,476
Gross amount at which carried at close of period, Land				93,669
Gross amount at which carried at close of period, Buildings and Improvements				103,564
Gross amount at which carried at close of period, Total	197,233			197,233
Accumulated depreciation and amortization	$ (11,771)			(11,771)
Date of construction	Dec. 31, 1973
Date acquired	Nov. 24, 2014
Real Estate:
Ending balance	$ 197,233
Accumulated Depreciation:
Ending balance	$ 11,771
425 Eye Street [Member] | Minimum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	5 years
425 Eye Street [Member] | Maximum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	40 years
Liberty Place [Member]
Real Estate And Accumulated Depreciation [Line Items]
Initial cost to company, Land				46,401
Initial cost to company, Building and Improvements				96,422
Costs capitalized subsequent to acquisition, Building and Improvements				11,675
Gross amount at which carried at close of period, Land				46,401
Gross amount at which carried at close of period, Buildings and Improvements				108,097
Gross amount at which carried at close of period, Total	$ 154,498			154,498
Accumulated depreciation and amortization	$ (10,569)			(10,569)
Date of construction	Dec. 31, 1993
Date acquired	Nov. 24, 2014
Real Estate:
Ending balance	$ 154,498
Accumulated Depreciation:
Ending balance	$ 10,569
Liberty Place [Member] | Minimum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	5 years
Liberty Place [Member] | Maximum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	40 years
1899 Pennsylvania Avenue [Member]
Real Estate And Accumulated Depreciation [Line Items]
Initial cost to company, Land				52,568
Initial cost to company, Building and Improvements				94,874
Costs capitalized subsequent to acquisition, Building and Improvements				4,160
Gross amount at which carried at close of period, Land				52,568
Gross amount at which carried at close of period, Buildings and Improvements				99,034
Gross amount at which carried at close of period, Total	$ 151,602			151,602
Accumulated depreciation and amortization	$ (9,263)			(9,263)
Date of construction	Dec. 31, 1915
Date acquired	Nov. 24, 2014
Real Estate:
Ending balance	$ 151,602
Accumulated Depreciation:
Ending balance	$ 9,263
1899 Pennsylvania Avenue [Member] | Minimum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	5 years
1899 Pennsylvania Avenue [Member] | Maximum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	40 years
2099 Pennsylvania Avenue [Member]
Real Estate And Accumulated Depreciation [Line Items]
Initial cost to company, Land				50,631
Initial cost to company, Building and Improvements				103,992
Costs capitalized subsequent to acquisition, Building and Improvements				17,230
Gross amount at which carried at close of period, Land				50,631
Gross amount at which carried at close of period, Buildings and Improvements				121,222
Gross amount at which carried at close of period, Total	$ 171,853			171,853
Accumulated depreciation and amortization	$ (11,014)			(11,014)
Date of construction	Dec. 31, 2001
Date acquired	Nov. 24, 2014
Real Estate:
Ending balance	$ 171,853
Accumulated Depreciation:
Ending balance	$ 11,014
2099 Pennsylvania Avenue [Member] | Minimum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	5 years
2099 Pennsylvania Avenue [Member] | Maximum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	40 years
Total Washington, D.C.
Real Estate And Accumulated Depreciation [Line Items]
Initial cost to company, Land				243,269
Initial cost to company, Building and Improvements				393,376
Costs capitalized subsequent to acquisition, Building and Improvements				38,541
Gross amount at which carried at close of period, Land				243,269
Gross amount at which carried at close of period, Buildings and Improvements				431,917
Gross amount at which carried at close of period, Total	$ 675,186			675,186
Accumulated depreciation and amortization	(42,617)			(42,617)
Real Estate:
Ending balance	675,186
Accumulated Depreciation:
Ending balance	42,617
One Market Plaza [Member]
Real Estate And Accumulated Depreciation [Line Items]
Encumbrances				975,000
Initial cost to company, Land				288,743
Initial cost to company, Building and Improvements				988,014
Costs capitalized subsequent to acquisition, Building and Improvements				62,007
Gross amount at which carried at close of period, Land				288,743
Gross amount at which carried at close of period, Buildings and Improvements				1,050,021
Gross amount at which carried at close of period, Total	1,338,764			1,338,764
Accumulated depreciation and amortization	$ (93,860)			(93,860)
Date of construction	Dec. 31, 1976
Date acquired	Nov. 24, 2014
Real Estate:
Ending balance	$ 1,338,764
Accumulated Depreciation:
Ending balance	$ 93,860
One Market Plaza [Member] | Minimum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	5 years
One Market Plaza [Member] | Maximum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	40 years
One Front Street [Member]
Real Estate And Accumulated Depreciation [Line Items]
Initial cost to company, Land				127,765
Initial cost to company, Building and Improvements				376,919
Costs capitalized subsequent to acquisition, Building and Improvements				3,293
Gross amount at which carried at close of period, Land				127,765
Gross amount at which carried at close of period, Buildings and Improvements				380,212
Gross amount at which carried at close of period, Total	$ 507,977			507,977
Accumulated depreciation and amortization	$ (13,113)			(13,113)
Date of construction	Dec. 31, 1979
Date acquired	Dec. 31, 2016
Real Estate:
Ending balance	$ 507,977
Accumulated Depreciation:
Ending balance	$ 13,113
One Front Street [Member] | Minimum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	5 years
One Front Street [Member] | Maximum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	40 years
50 Beale Street [Member]
Real Estate And Accumulated Depreciation [Line Items]
Encumbrances				228,000
Initial cost to company, Land				141,097
Initial cost to company, Building and Improvements				343,819
Costs capitalized subsequent to acquisition, Building and Improvements				567
Gross amount at which carried at close of period, Land				141,097
Gross amount at which carried at close of period, Buildings and Improvements				344,386
Gross amount at which carried at close of period, Total	$ 485,483			485,483
Accumulated depreciation and amortization	$ (5,111)			(5,111)
Date of construction	Dec. 31, 1968
Date acquired	Jul. 17, 2017
Real Estate:
Ending balance	$ 485,483
Accumulated Depreciation:
Ending balance	$ 5,111
50 Beale Street [Member] | Minimum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	5 years
50 Beale Street [Member] | Maximum
Real Estate And Accumulated Depreciation [Line Items]
Life on which depreciation in latest income statement is computed	40 years
Total San Francisco
Real Estate And Accumulated Depreciation [Line Items]
Encumbrances				1,203,000
Initial cost to company, Land				557,605
Initial cost to company, Building and Improvements				1,708,752
Costs capitalized subsequent to acquisition, Building and Improvements				65,867
Gross amount at which carried at close of period, Land				557,605
Gross amount at which carried at close of period, Buildings and Improvements				1,774,619
Gross amount at which carried at close of period, Total	$ 2,332,224			2,332,224
Accumulated depreciation and amortization	(112,084)			$ (112,084)
Real Estate:
Ending balance	2,332,224
Accumulated Depreciation:
Ending balance	$ 112,084