Segment Reporting - Segment Revenue and Profit or Loss Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Rental revenue	$ 115,634	$ 110,903	$ 343,155	$ 333,827
Intercompany rental revenue	0	0	0	0
Tenant expense reimbursement	19,176	23,096	56,350	59,878
Observatory revenue	38,093	35,702	91,112	84,525
Construction revenue	0	0	0	1,981
Third-party management and other fees	404	618	1,372	1,658
Other revenue and fees	2,541	5,460	6,748	10,565
Total revenues	175,848	175,779	498,737	492,434
Operating expenses:
Property operating expenses	38,585	41,052	115,075	120,341
Intercompany rent expense	0	0	0	0
Ground rent expenses	2,331	2,331	6,994	6,994
General and administrative expenses	11,798	10,182	35,623	28,395
Observatory expenses	7,250	7,896	21,900	23,391
Construction expenses	0	0	0	3,222
Real estate taxes	24,691	23,613	71,773	69,543
Acquisition expenses	0	193	98	193
Depreciation and amortization	37,607	45,169	115,382	126,216
Total operating expenses	122,262	130,436	366,845	378,295
Total operating income (loss)	53,586	45,343	131,892	114,139
Interest expense	(17,939)	(16,680)	(53,310)	(50,298)
Income (loss) before income taxes	35,647	28,663	78,582	63,841
Income tax benefit (expense)	(2,750)	(2,578)	(4,340)	(3,283)
Net income (loss)	32,897	26,085	74,242	60,558
Segment assets	3,882,569	3,308,767	3,882,569	3,308,767	$ 3,300,650
Expenditures for segment assets	52,828	40,102	140,099	109,315
Operating segments | Real Estate
Segment Reporting Information [Line Items]
Rental revenue	115,634	110,903	343,155	333,827
Intercompany rental revenue	22,983	20,828	55,189	51,402
Tenant expense reimbursement	19,176	23,096	56,350	59,878
Observatory revenue	0	0	0	0
Construction revenue				0
Third-party management and other fees	404	618	1,372	1,658
Other revenue and fees	2,536	5,460	6,738	10,565
Total revenues	160,733	160,905	462,804	457,330
Operating expenses:
Property operating expenses	38,585	41,052	115,075	120,341
Intercompany rent expense	0	0	0	0
Ground rent expenses	2,331	2,331	6,994	6,994
General and administrative expenses	11,798	10,182	35,623	28,395
Observatory expenses	0	0	0	0
Construction expenses				0
Real estate taxes	24,691	23,613	71,773	69,543
Acquisition expenses		193	98	193
Depreciation and amortization	37,421	45,072	115,002	125,847
Total operating expenses	114,826	122,443	344,565	351,313
Total operating income (loss)	45,907	38,462	118,239	106,017
Interest expense	(17,939)	(16,680)	(53,310)	(50,298)
Income (loss) before income taxes	27,968	21,782	64,929	55,719
Income tax benefit (expense)	(332)	(474)	(1,018)	(1,247)
Net income (loss)	27,636	21,308	63,911	54,472
Segment assets	3,636,262	3,070,234	3,636,262	3,070,234
Expenditures for segment assets	52,828	39,915	140,052	109,104
Operating segments | Observatory
Segment Reporting Information [Line Items]
Rental revenue	0	0	0	0
Intercompany rental revenue	0	0	0	0
Tenant expense reimbursement	0	0	0	0
Observatory revenue	38,093	35,702	91,112	84,525
Construction revenue				0
Third-party management and other fees	0	0	0	0
Other revenue and fees	5	0	10	0
Total revenues	38,098	35,702	91,122	84,525
Operating expenses:
Property operating expenses	0	0	0	0
Intercompany rent expense	22,983	20,828	55,189	51,402
Ground rent expenses	0	0	0	0
General and administrative expenses	0	0	0	0
Observatory expenses	7,250	7,896	21,900	23,391
Construction expenses				0
Real estate taxes	0	0	0	0
Acquisition expenses		0	0	0
Depreciation and amortization	186	97	380	268
Total operating expenses	30,419	28,821	77,469	75,061
Total operating income (loss)	7,679	6,881	13,653	9,464
Interest expense	0	0	0	0
Income (loss) before income taxes	7,679	6,881	13,653	9,464
Income tax benefit (expense)	(2,418)	(2,104)	(3,322)	(2,376)
Net income (loss)	5,261	4,777	10,331	7,088
Segment assets	246,307	235,937	246,307	235,937
Expenditures for segment assets	0	187	47	211
Operating segments | Other
Segment Reporting Information [Line Items]
Rental revenue		0		0
Intercompany rental revenue		0		0
Tenant expense reimbursement		0		0
Observatory revenue		0		0
Construction revenue				5,696
Third-party management and other fees		0		0
Other revenue and fees		0		0
Total revenues		0		5,696
Operating expenses:
Property operating expenses		0		0
Intercompany rent expense		0		0
Ground rent expenses		0		0
General and administrative expenses		0		0
Observatory expenses		0		0
Construction expenses				6,539
Real estate taxes		0		0
Acquisition expenses		0		0
Depreciation and amortization		0		101
Total operating expenses		0		6,640
Total operating income (loss)		0		(944)
Interest expense		0		0
Income (loss) before income taxes		0		(944)
Income tax benefit (expense)		0		340
Net income (loss)		0		(604)
Segment assets		2,596		2,596
Expenditures for segment assets		0		0
Intersegment Elimination
Segment Reporting Information [Line Items]
Rental revenue	0	0	0	0
Intercompany rental revenue	(22,983)	(20,828)	(55,189)	(51,402)
Tenant expense reimbursement	0	0	0	0
Observatory revenue	0	0	0	0
Construction revenue				(3,715)
Third-party management and other fees	0	0	0	0
Other revenue and fees	0	0	0	0
Total revenues	(22,983)	(20,828)	(55,189)	(55,117)
Operating expenses:
Property operating expenses	0	0	0	0
Intercompany rent expense	(22,983)	(20,828)	(55,189)	(51,402)
Ground rent expenses	0	0	0	0
General and administrative expenses	0	0	0	0
Observatory expenses	0	0	0	0
Construction expenses				(3,317)
Real estate taxes	0	0	0	0
Acquisition expenses		0	0	0
Depreciation and amortization	0	0	0	0
Total operating expenses	(22,983)	(20,828)	(55,189)	(54,719)
Total operating income (loss)	0	0	0	(398)
Interest expense	0	0	0	0
Income (loss) before income taxes	0	0	0	(398)
Income tax benefit (expense)	0	0	0	0
Net income (loss)	0	0	0	(398)
Segment assets	0	0	0	0
Expenditures for segment assets	$ 0	$ 0	$ 0	$ 0