Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Commercial real estate properties, at cost:
Land	$ 201,196	$ 201,196
Development costs	7,986	7,951
Building and improvements	2,458,473	2,249,482
Commercial real estate properties, at cost, gross	2,667,655	2,458,629
Less: accumulated depreciation	(656,900)	(556,546)
Commercial real estate properties, net	2,010,755	1,902,083
Cash and cash equivalents	464,344	554,371
Restricted cash	65,853	61,514
Tenant and other receivables, net of allowance of $1,422 and $3,333 in 2017 and 2016, respectively	28,329	22,542
Deferred rent receivables, net of allowance of $185 and $390 in 2017 and 2016, respectively	178,629	152,074
Prepaid expenses and other assets	61,028	53,749
Deferred costs, net	262,701	277,081
Acquired below market ground leases, net	368,229	376,060
Goodwill	491,479	491,479
Total assets	3,931,347	3,890,953
Liabilities:
Mortgage notes payable, net	717,164	759,016
Senior unsecured notes, net	707,895	590,388
Unsecured term loan facility, net	263,662	262,927
Unsecured revolving credit facility	0	0
Accounts payable and accrued expenses	110,849	134,064
Acquired below market leases, net	66,047	82,300
Deferred revenue and other liabilities	40,907	32,212
Tenants’ security deposits	47,086	47,183
Total liabilities	1,953,610	1,908,090
Commitments and contingencies
Capital:
Private perpetual preferred units, $16.62 per unit liquidation preference, 1,560,360 issued and outstanding in 2017 and 2016, respectively	8,004	8,004
Total capital	1,977,737	1,982,863
Total liabilities and capital	3,931,347	3,890,953
Series PR Operating Partnership Units [Member]
Capital:
ESRT partners' capital (3,004,095 and 2,990,931 general partner operating partnership units and 158,472,949 and 152,849,546 limited partner operating partnership units outstanding at December 31, 2017 and 2016, respectively)	1,168,282	1,154,136
Limited partner operating partnership units	778,279	793,360
Series ES Operating Partnership Units [Member]
Capital:
Limited partner operating partnership units	17,132	20,091
Series 60 Operating Partnership Units [Member]
Capital:
Limited partner operating partnership units	3,992	4,880
Series 250 Operating Partnership Units [Member]
Capital:
Limited partner operating partnership units	$ 2,048	$ 2,392