Segment Reporting - Components of Segment Profit for Each Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Revenues:
Rental revenue	$ 141,071		$ 284,488
Rental revenue		$ 124,038		$ 246,349
Intercompany rental revenue	0	0	0	0
Tenant expense reimbursement	0	16,205	0	33,999
Observatory revenue	32,895	35,201	53,464	56,450
Lease termination fees	363	357	751	979
Third-party management and other fees	331	376	651	839
Other revenue and fees	1,584	2,352	4,183	7,184
Total revenues	176,244	178,529	343,537	345,800
Operating expenses:
Property operating expenses	40,227	39,418	83,182	83,603
Intercompany rent expense	0	0	0	0
Ground rent expenses	2,332	2,332	4,663	4,663
General and administrative expenses	15,998	13,225	30,024	25,853
Observatory expenses	8,360	7,678	15,935	15,014
Real estate taxes	28,267	26,743	56,499	53,487
Depreciation and amortization	44,821	39,468	90,919	79,351
Total operating expenses	140,005	128,864	281,222	261,971
Total operating income	36,239	49,665	62,315	83,829
Other income (expense):
Interest income	3,899	2,499	7,638	3,724
Interest expense	(20,597)	(20,525)	(41,286)	(38,116)
Income before income taxes	19,541	31,639	28,667	49,437
Income tax (expense) benefit	(611)	(1,455)	119	(1,195)
Net income	18,930	30,184	28,786	48,242
Segment assets	4,155,575	4,162,905	4,155,575	4,162,905	$ 4,195,780
Expenditures for segment assets	61,972	76,889	120,292	123,239
Intersegment Elimination
Revenues:
Rental revenue	0		0
Rental revenue		0		0
Intercompany rental revenue	(21,491)	(21,990)	(35,512)	(35,551)
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	(21,491)	(21,990)	(35,512)	(35,551)
Operating expenses:
Property operating expenses	0	0	0	0
Intercompany rent expense	(21,491)	(21,990)	(35,512)	(35,551)
Ground rent expenses	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	(21,491)	(21,990)	(35,512)	(35,551)
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) benefit	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	141,071		284,488
Rental revenue		124,038		246,349
Intercompany rental revenue	21,491	21,990	35,512	35,551
Tenant expense reimbursement		16,205		33,999
Observatory revenue	0	0	0	0
Lease termination fees	363	357	751	979
Third-party management and other fees	331	376	651	839
Other revenue and fees	1,584	2,352	4,183	7,184
Total revenues	164,840	165,318	325,585	324,901
Operating expenses:
Property operating expenses	40,227	39,418	83,182	83,603
Intercompany rent expense	0	0	0	0
Ground rent expenses	2,332	2,332	4,663	4,663
General and administrative expenses	15,998	13,225	30,024	25,853
Observatory expenses	0	0	0	0
Real estate taxes	28,267	26,743	56,499	53,487
Depreciation and amortization	44,813	39,452	90,904	79,317
Total operating expenses	131,637	121,170	265,272	246,923
Total operating income	33,203	44,148	60,313	77,978
Other income (expense):
Interest income	3,899	2,499	7,638	3,724
Interest expense	(20,597)	(20,525)	(41,286)	(38,116)
Income before income taxes	16,505	26,122	26,665	43,586
Income tax (expense) benefit	(261)	(268)	(495)	(575)
Net income	16,244	25,854	26,170	43,011
Segment assets	3,891,038	3,902,676	3,891,038	3,902,676
Expenditures for segment assets	47,433	61,017	91,964	95,816
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	32,895	35,201	53,464	56,450
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	32,895	35,201	53,464	56,450
Operating expenses:
Property operating expenses	0	0	0	0
Intercompany rent expense	21,491	21,990	35,512	35,551
Ground rent expenses	0	0	0	0
General and administrative expenses	0	0	0	0
Observatory expenses	8,360	7,678	15,935	15,014
Real estate taxes	0	0	0	0
Depreciation and amortization	8	16	15	34
Total operating expenses	29,859	29,684	51,462	50,599
Total operating income	3,036	5,517	2,002	5,851
Other income (expense):
Interest income	0	0	0	0
Interest expense	0	0	0	0
Income before income taxes	3,036	5,517	2,002	5,851
Income tax (expense) benefit	(350)	(1,187)	614	(620)
Net income	2,686	4,330	2,616	5,231
Segment assets	264,537	260,229	264,537	260,229
Expenditures for segment assets	$ 14,539	$ 15,872	$ 28,328	$ 27,423