Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Schedule of estimated useful lives

Properties other than Right of use assets - operating leases are depreciated using the straight-line method over the estimated useful lives of the assets. The estimated useful lives are as follows:

Category	Term
Building (fee ownership)	40 years
Building improvements	shorter of remaining life of the building or useful life
Building (leasehold interest)	lesser of 40 years or remaining term of the lease
Right of use assets - financing leases	lesser of 40 years or remaining lease term
Furniture and fixtures	4 to 7 years
Tenant improvements	shorter of remaining term of the lease or useful life

Summary of identified intangible assets (acquired above-market leases and in-place leases) and intangible liabilities (acquired below-market leases)

The following summarizes our identified intangible assets (acquired above-market leases and in-place leases) and intangible liabilities (acquired below-market leases) as of December 31, 2020 and 2019 (in thousands):

	December 31,
	2020		2019
Identified intangible assets (included in other assets):
Gross amount	$	215,673	$	255,198
Accumulated amortization	(190,523)		(228,223)
Net (1)	$	25,150	$	26,975
Identified intangible liabilities (included in deferred revenue):
Gross amount	$	241,409	$	282,048
Accumulated amortization	(230,479)		(249,514)
Net (1)	$	10,930	$	32,534

(1)    As of December 31, 2020, no net intangible assets and no net intangible liabilities were reclassified to assets held for sale and liabilities related to assets held for sale. As of December 31, 2019, no net intangible assets and no net intangible liabilities were reclassified to assets held for sale and liabilities related to assets held for sale.

Schedule of estimated annual amortization of acquired above-market leases, net of acquired below-market leases

The estimated annual amortization of acquired above-market leases, net of acquired (below-market) leases (a component of rental revenue), for each of the five succeeding years is as follows (in thousands):    

2021	(1,403)
2022	(119)
2023	91
2024	258
2025	781

Schedule of estimated annual amortization of all other identifiable assets

The estimated annual amortization of all other identifiable assets (a component of depreciation and amortization expense) including tenant improvements for each of the five succeeding years is as follows (in thousands):

2021	4,899
2022	3,456
2023	2,841
2024	2,520
2025	1,427

Schedule of marketable securities

At December 31, 2020 and 2019, we held the following marketable securities (in thousands):

	December 31,
	2020		2019
Commercial mortgage-backed securities	$	28,570	$	29,887
Total marketable securities available-for-sale	$	28,570	$	29,887

Schedules of concentration of risk, by risk factor

For the years ended December 31, 2020, 2019, and 2018, the following properties contributed more than 5.0% of our annualized cash rent from office properties, including our share of annualized cash rent from joint venture office properties:

Property	2020	Property	2019	Property	2018
11 Madison Avenue	8.2%	1185 Avenue of the Americas	7.6%	11 Madison Avenue	7.4%
420 Lexington Ave (Graybar)	7.5%	11 Madison Avenue	7.4%	1185 Avenue of the Americas	6.7%
1185 Avenue of the Americas	6.9%	420 Lexington Avenue	6.6%	420 Lexington Avenue	6.5%
1515 Broadway	6.6%	1515 Broadway	6.1%	1515 Broadway	6.0%
220 East 42nd Street	5.9%	One Madison Avenue	6.0%	One Madison Avenue	5.8%
280 Park Avenue	5.4%	220 East 42nd Street	5.5%