Condensed Consolidated Statements of Income (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues:
Total revenues	$ 178,529	$ 176,349	$ 345,800	$ 340,682
Operating expenses:
Property operating expenses	39,418	38,529	83,603	80,739
Ground rent expenses	2,332	2,332	4,663	4,663
General and administrative expenses	13,225	12,579	25,853	23,667
Observatory expenses	7,678	7,176	15,014	14,431
Real estate taxes	26,743	24,542	53,487	49,100
Depreciation and amortization	39,468	40,532	79,351	81,378
Total operating expenses	128,864	125,690	261,971	253,978
Total operating income	49,665	50,659	83,829	86,704
Other income (expense):
Interest income	2,499	775	3,724	1,396
Interest expense	(20,525)	(17,477)	(38,116)	(35,219)
Loss from derivative financial instruments	0	(42)	0	(289)
Income before income taxes	31,639	33,915	49,437	52,592
Income tax expense	(1,455)	(2,556)	(1,195)	(2,088)
Net income	30,184	31,359	48,242	50,504
Private perpetual preferred unit distributions	(234)	(234)	(468)	(468)
Net income attributable to common unitholders	$ 29,950	$ 31,125	$ 47,774	$ 50,036
Total weighted average units:
Basic (in units)	297,244	296,388	297,028	296,388
Diluted (in units)	297,244	298,398	297,029	298,180
Earnings per unit attributable to common unitholders:
Basic earnings (in USD per unit)	$ 0.10	$ 0.10	$ 0.16	$ 0.17
Diluted earnings (in USD per unit)	0.10	0.10	0.16	0.17
Dividends per unit (in USD per unit)	$ 0.105	$ 0.105	$ 0.21	$ 0.21
Rental revenue
Revenues:
Total revenues	$ 124,038	$ 120,844	$ 246,349	$ 237,957
Tenant expense reimbursement
Revenues:
Total revenues	16,205	17,569	33,999	33,543
Observatory revenue
Revenues:
Total revenues	35,201	33,966	56,450	54,906
Lease termination fees
Revenues:
Total revenues	357	1,251	979	9,189
Third-party management and other fees
Revenues:
Total revenues	376	392	839	743
Other revenue and fees
Revenues:
Total revenues	$ 2,352	$ 2,327	$ 7,184	$ 4,344