Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Rental revenue													$ 460,653	$ 447,784	$ 400,825
Tenant expense reimbursement													73,459	79,516	67,651
Observatory revenue													124,814	112,172	111,541
Construction revenue													0	1,981	38,648
Third-party management and other fees													1,766	2,133	2,376
Other revenue and fees													17,308	14,048	14,285
Total revenues	$ 179,263	$ 175,848	$ 165,815	$ 157,074	$ 165,200	$ 175,779	$ 164,773	$ 151,882	$ 170,411	$ 169,441	$ 155,168	$ 140,306	678,000	657,634	635,326
Operating expenses:
Property operating expenses													153,850	158,638	148,676
Ground rent expenses													9,326	9,326	5,339
General and administrative expenses													49,078	38,073	39,037
Observatory expenses													29,833	32,174	31,413
Construction expenses													0	3,222	38,596
Real estate taxes													96,061	93,165	82,131
Acquisition expenses													98	193	3,382
Depreciation and amortization													155,211	171,474	145,431
Total operating expenses													493,457	506,265	494,005
Total operating income (loss)	52,651	53,586	44,192	34,114	37,230	45,343	45,039	23,757	31,282	43,412	42,539	24,088	184,543	151,369	141,321
Interest expense													(71,147)	(67,492)	(66,456)
Income before income taxes													113,396	83,877	74,865
Income tax expense													(6,146)	(3,949)	(4,655)
Net income	$ 33,008	$ 32,897	$ 24,640	$ 16,705	$ 19,370	$ 26,085	$ 26,585	$ 7,888	$ 10,964	$ 22,734	$ 25,281	$ 11,231	107,250	79,928	70,210
Private perpetual preferred unit distributions													(936)	(936)	(476)
Net income attributable to non-controlling interests													(54,858)	(45,262)	(43,067)
Net income attributable to common stockholders													$ 51,456	$ 33,730	$ 26,667
Total weighted average shares:
Basic (in shares)													133,881	114,245	97,941
Diluted (in shares)													277,568	266,621	254,506
Net income per share attributable to common stockholders:
Basic (USD per share)													$ 0.38	$ 0.30	$ 0.27
Diluted (USD per share)													$ 0.38	$ 0.29	$ 0.27