Segment Reporting - Components of Segment Profit for Each Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Revenues:
Rental revenue	$ 150,225		$ 434,713
Rental revenue		$ 123,621		$ 369,970
Intercompany rental revenue	0	0	0	0
Tenant expense reimbursement	0	18,627	0	52,626
Observatory revenue	37,575	40,241	91,039	96,691
Lease termination fees	2,361	1,185	3,112	2,164
Third-party management and other fees	304	312	955	1,151
Other revenue and fees	2,408	2,416	6,591	9,600
Total revenues	192,873	186,402	536,410	532,202
Operating expenses:
Property operating expenses	47,894	42,772	131,076	126,375
Intercompany rent expense	0	0	0	0
Ground rent expense	2,331	2,331	6,994	6,994
General and administrative expenses	14,421	13,148	44,445	39,001
Observatory expenses	9,089	8,854	25,024	23,868
Real estate taxes	29,599	28,284	86,098	81,771
Depreciation and amortization	44,260	42,475	135,179	121,826
Total operating expenses	147,594	137,864	428,816	399,835
Total operating income	45,279	48,538	107,594	132,367
Other income (expense):
Interest income	2,269	3,485	9,907	7,209
Interest expense	(19,426)	(20,658)	(60,712)	(58,774)
Income before income taxes	28,122	31,365	56,789	80,802
Income tax expense	(1,338)	(2,135)	(1,219)	(3,330)
Net income	26,784	29,230	55,570	77,472
Segment assets	3,925,317	4,166,832	3,925,317	4,166,832	$ 4,195,780
Expenditures for segment assets	61,276	67,120	181,568	190,359
Intersegment Elimination
Revenues:
Rental revenue	0		0
Rental revenue		0		0
Intercompany rental revenue	(23,242)	(23,805)	(58,754)	(59,356)
Tenant expense reimbursement		0		0
Observatory revenue	0	0	0	0
Lease termination fees	0	0	0	0
Third-party management and other fees	0	0	0	0
Other revenue and fees	0	0	0	0
Total revenues	(23,242)	(23,805)	(58,754)	(59,356)
Operating expenses:
Property operating expenses	0	0	0	0
Intercompany rent expense	(23,242)	(23,805)	(58,754)	(59,356)
Ground rent expense	0	0	0	0
General and administrative expenses	0	0	0	0
Observatory expenses	0	0	0	0
Real estate taxes	0	0	0	0
Depreciation and amortization	0	0	0	0
Total operating expenses	(23,242)	(23,805)	(58,754)	(59,356)
Total operating income	0	0	0	0
Other income (expense):
Interest income	0	0	0	0
Interest expense	0	0	0	0
Income before income taxes	0	0	0	0
Income tax expense	0	0	0	0
Net income	0	0	0	0
Segment assets	0	0	0	0
Expenditures for segment assets	0	0	0	0
Real Estate | Operating Segments
Revenues:
Rental revenue	150,225		434,713
Rental revenue		123,621		369,970
Intercompany rental revenue	23,242	23,805	58,754	59,356
Tenant expense reimbursement		18,627		52,626
Observatory revenue	0	0	0	0
Lease termination fees	2,361	1,185	3,112	2,164
Third-party management and other fees	304	312	955	1,151
Other revenue and fees	2,408	2,416	6,591	9,600
Total revenues	178,540	169,966	504,125	494,867
Operating expenses:
Property operating expenses	47,894	42,772	131,076	126,375
Intercompany rent expense	0	0	0	0
Ground rent expense	2,331	2,331	6,994	6,994
General and administrative expenses	14,421	13,148	44,445	39,001
Observatory expenses	0	0	0	0
Real estate taxes	29,599	28,284	86,098	81,771
Depreciation and amortization	44,253	42,458	135,157	121,775
Total operating expenses	138,498	128,993	403,770	375,916
Total operating income	40,042	40,973	100,355	118,951
Other income (expense):
Interest income	2,269	3,485	9,907	7,209
Interest expense	(19,426)	(20,658)	(60,712)	(58,774)
Income before income taxes	22,885	23,800	49,550	67,386
Income tax expense	(267)	(277)	(762)	(852)
Net income	22,618	23,523	48,788	66,534
Segment assets	3,659,592	3,904,454	3,659,592	3,904,454
Expenditures for segment assets	42,901	52,613	134,865	148,429
Observatory | Operating Segments
Revenues:
Rental revenue	0		0
Rental revenue		0		0
Intercompany rental revenue	0	0	0	0
Tenant expense reimbursement		0		0
Observatory revenue	37,575	40,241	91,039	96,691
Lease termination fees	0	0	0	0
Third-party management and other fees	0	0	0	0
Other revenue and fees	0	0	0	0
Total revenues	37,575	40,241	91,039	96,691
Operating expenses:
Property operating expenses	0	0	0	0
Intercompany rent expense	23,242	23,805	58,754	59,356
Ground rent expense	0	0	0	0
General and administrative expenses	0	0	0	0
Observatory expenses	9,089	8,854	25,024	23,868
Real estate taxes	0	0	0	0
Depreciation and amortization	7	17	22	51
Total operating expenses	32,338	32,676	83,800	83,275
Total operating income	5,237	7,565	7,239	13,416
Other income (expense):
Interest income	0	0	0	0
Interest expense	0	0	0	0
Income before income taxes	5,237	7,565	7,239	13,416
Income tax expense	(1,071)	(1,858)	(457)	(2,478)
Net income	4,166	5,707	6,782	10,938
Segment assets	265,725	262,378	265,725	262,378
Expenditures for segment assets	$ 18,375	$ 14,507	$ 46,703	$ 41,930