Segment Reporting - Components of Segment Profit for Each Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Revenues:
Rental revenue	$ 143,417
Rental revenue		$ 122,311
Intercompany rental revenue	0	0
Tenant expense reimbursement	0	17,794
Observatory revenue	20,569	21,249
Lease termination fees	388	622
Third-party management and other fees	320	463
Other revenue and fees	2,599	4,832
Total revenues	167,293	167,271
Operating expenses:
Property operating expenses	42,955	44,185
Intercompany rent expense	0	0
Ground rent expenses	2,331	2,331
General and administrative expenses	14,026	12,628
Observatory expenses	7,575	7,336
Real estate taxes	28,232	26,744
Depreciation and amortization	46,098	39,883
Total operating expenses	141,217	133,107
Total operating income (loss)	26,076	34,164
Other income (expense):
Interest income	3,739	1,225
Interest expense	(20,689)	(17,591)
Income (loss) before income taxes	9,126	17,798
Income tax benefit (expense)	730	260
Net income (loss)	9,856	18,058
Segment assets	4,192,440	4,141,813	$ 4,195,780
Expenditures for segment assets	58,320	46,350
Intersegment Elimination
Revenues:
Rental revenue	0
Rental revenue		0
Intercompany rental revenue	(14,021)	(13,561)
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	(14,021)	(13,561)
Operating expenses:
Property operating expenses	0	0
Intercompany rent expense	(14,021)	(13,561)
Ground rent expenses	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	(14,021)	(13,561)
Total operating income (loss)	0	0
Other income (expense):
Interest income	0	0
Interest expense	0	0
Income (loss) before income taxes	0	0
Income tax benefit (expense)	0	0
Net income (loss)	0	0
Segment assets	0	0
Expenditures for segment assets	0	0
Real Estate | Operating Segments
Revenues:
Rental revenue	143,417
Rental revenue		122,311
Intercompany rental revenue	14,021	13,561
Tenant expense reimbursement		17,794
Observatory revenue	0	0
Lease termination fees	388	622
Third-party management and other fees	320	463
Other revenue and fees	2,599	4,832
Total revenues	160,745	159,583
Operating expenses:
Property operating expenses	42,955	44,185
Intercompany rent expense	0	0
Ground rent expenses	2,331	2,331
General and administrative expenses	14,026	12,628
Observatory expenses	0	0
Real estate taxes	28,232	26,744
Depreciation and amortization	46,091	39,865
Total operating expenses	133,635	125,753
Total operating income (loss)	27,110	33,830
Other income (expense):
Interest income	3,739	1,225
Interest expense	(20,689)	(17,591)
Income (loss) before income taxes	10,160	17,464
Income tax benefit (expense)	(234)	(307)
Net income (loss)	9,926	17,157
Segment assets	3,930,697	3,887,337
Expenditures for segment assets	44,531	34,797
Observatory | Operating Segments
Revenues:
Rental revenue	0
Rental revenue		0
Intercompany rental revenue	0	0
Tenant expense reimbursement		0
Observatory revenue	20,569	21,249
Lease termination fees	0	0
Third-party management and other fees	0	0
Other revenue and fees	0	0
Total revenues	20,569	21,249
Operating expenses:
Property operating expenses	0	0
Intercompany rent expense	14,021	13,561
Ground rent expenses	0	0
General and administrative expenses	0	0
Observatory expenses	7,575	7,336
Real estate taxes	0	0
Depreciation and amortization	7	18
Total operating expenses	21,603	20,915
Total operating income (loss)	(1,034)	334
Other income (expense):
Interest income	0	0
Interest expense	0	0
Income (loss) before income taxes	(1,034)	334
Income tax benefit (expense)	964	567
Net income (loss)	(70)	901
Segment assets	261,743	254,476
Expenditures for segment assets	$ 13,789	$ 11,553