Segment Reporting - Components of Segment Profit for Each Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Revenues:
Rental revenue	$ 148,113	$ 143,417
Intercompany rental revenue	0	0
Tenant expense reimbursement		0
Observatory revenue	19,544	20,569
Lease termination fees	211	388
Third-party management and other fees	346	320
Other revenue and fees	2,010	2,599
Total revenues	170,224	167,293
Operating expenses:
Property operating expenses	41,468	42,955
Intercompany rent expense	0	0
Ground rent expense	2,331	2,331
General and administrative expenses	15,951	14,026
Observatory expenses	8,154	7,575
Real estate taxes	29,254	28,232
Depreciation and amortization	46,093	46,098
Total operating expenses	143,251	141,217
Total operating income	26,973	26,076
Other income (expense):
Interest income	637	3,739
Interest expense	(19,618)	(20,689)
Loss on early extinguishment of debt	(86)	0
Income before income taxes	7,906	9,126
Income tax (expense) benefit	382	730
Net income	8,288	9,856
Segment assets	4,664,558	4,192,440	$ 3,931,834
Expenditures for segment assets	27,807	58,320
Intersegment Elimination
Revenues:
Rental revenue	0	0
Intercompany rental revenue	(11,536)	(14,021)
Tenant expense reimbursement		0
Observatory revenue	0	0
Lease termination fees	0	0
Third-party management and other fees	0	0
Other revenue and fees	0	0
Total revenues	(11,536)	(14,021)
Operating expenses:
Property operating expenses	0	0
Intercompany rent expense	(11,536)	(14,021)
Ground rent expense	0	0
General and administrative expenses	0	0
Observatory expenses	0	0
Real estate taxes	0	0
Depreciation and amortization	0	0
Total operating expenses	(11,536)	(14,021)
Total operating income	0	0
Other income (expense):
Interest income	0	0
Interest expense	0	0
Loss on early extinguishment of debt	0
Income before income taxes	0	0
Income tax (expense) benefit	0	0
Net income	0	0
Segment assets	0	0
Expenditures for segment assets	0	0
Real Estate | Operating Segments
Revenues:
Rental revenue	148,113	143,417
Intercompany rental revenue	11,536	14,021
Tenant expense reimbursement		0
Observatory revenue	0	0
Lease termination fees	211	388
Third-party management and other fees	346	320
Other revenue and fees	2,010	2,599
Total revenues	162,216	160,745
Operating expenses:
Property operating expenses	41,468	42,955
Intercompany rent expense	0	0
Ground rent expense	2,331	2,331
General and administrative expenses	15,951	14,026
Observatory expenses	0	0
Real estate taxes	29,254	28,232
Depreciation and amortization	46,085	46,091
Total operating expenses	135,089	133,635
Total operating income	27,127	27,110
Other income (expense):
Interest income	637	3,739
Interest expense	(19,618)	(20,689)
Loss on early extinguishment of debt	(86)
Income before income taxes	8,060	10,160
Income tax (expense) benefit	(227)	(234)
Net income	7,833	9,926
Segment assets	4,409,281	3,930,697
Expenditures for segment assets	26,570	44,531
Observatory | Operating Segments
Revenues:
Rental revenue	0	0
Intercompany rental revenue	0	0
Tenant expense reimbursement		0
Observatory revenue	19,544	20,569
Lease termination fees	0	0
Third-party management and other fees	0	0
Other revenue and fees	0	0
Total revenues	19,544	20,569
Operating expenses:
Property operating expenses	0	0
Intercompany rent expense	11,536	14,021
Ground rent expense	0	0
General and administrative expenses	0	0
Observatory expenses	8,154	7,575
Real estate taxes	0	0
Depreciation and amortization	8	7
Total operating expenses	19,698	21,603
Total operating income	(154)	(1,034)
Other income (expense):
Interest income	0	0
Interest expense	0	0
Loss on early extinguishment of debt	0
Income before income taxes	(154)	(1,034)
Income tax (expense) benefit	609	964
Net income	455	(70)
Segment assets	255,277	261,743
Expenditures for segment assets	$ 1,237	$ 13,789