Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Rental revenue													$ 586,414
Rental revenue														$ 493,231	$ 483,944
Tenant expense reimbursement													0	72,372	73,679
Observatory revenue													128,769	131,227	127,118
Lease termination fees													4,352	20,847	13,551
Third-party management and other fees													1,254	1,440	1,400
Other revenue and fees													10,554	12,394	9,834
Total revenues	$ 194,933	$ 192,873	$ 176,244	$ 167,293	$ 199,309	$ 186,402	$ 178,529	$ 167,271	$ 182,297	$ 186,547	$ 176,349	$ 164,333	731,343	731,511	709,526
Operating expenses:
Property operating expenses													174,977	167,379	163,531
Ground rent expenses													9,326	9,326	9,326
General and administrative expenses													61,063	52,674	50,315
Observatory expenses													33,767	32,767	30,275
Real estate taxes													115,916	110,000	102,466
Depreciation and amortization													181,588	168,508	160,710
Total operating expenses													576,637	540,654	516,623
Total operating income	47,112	45,279	36,239	26,076	58,490	48,538	49,665	34,164	50,191	56,008	50,659	36,045	154,706	190,857	192,903
Other income (expense):
Interest income													11,259	10,661	2,942
Interest expense													(79,246)	(79,623)	(68,473)
Loss on early extinguishment of debt													0	0	(2,157)
Loss from derivative financial instruments													0	0	(289)
Income before income taxes													86,719	121,895	124,926
Income tax expense													(2,429)	(4,642)	(6,673)
Net income	$ 28,720	$ 26,784	$ 18,930	$ 9,856	$ 39,781	$ 29,230	$ 30,184	$ 18,058	$ 32,260	$ 35,489	$ 31,359	$ 19,145	84,290	117,253	118,253
Private perpetual preferred unit distributions													(1,743)	(936)	(936)
Net income attributable to non-controlling interests													(33,102)	(50,714)	(54,670)
Net income attributable to common stockholders													$ 49,445	$ 65,603	$ 62,647
Total weighted average shares:
Basic (in shares)													178,340	167,571	158,380
Diluted (in shares)													297,798	297,259	298,049
Earnings per share attributable to common stockholders:
Basic (USD per share)													$ 0.28	$ 0.39	$ 0.40
Diluted (USD per share)													$ 0.28	$ 0.39	$ 0.39