Condensed Consolidated Statements of Income (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues:
Rental revenue	$ 123,621	$ 122,391	$ 369,970	$ 360,348
Tenant expense reimbursement	18,627	20,346	52,626	53,889
Observatory revenue	40,241	39,306	96,691	94,212
Lease termination fees	1,185	1,165	2,164	10,354
Third-party management and other fees	312	345	1,151	1,088
Other revenue and fees	2,416	2,993	9,600	7,338
Total revenues	186,402	186,546	532,202	527,229
Operating expenses:
Property operating expenses	42,772	41,270	126,375	122,009
Ground rent expenses	2,331	2,331	6,994	6,994
General and administrative expenses	13,148	12,899	39,001	36,566
Observatory expenses	8,854	8,648	23,868	23,079
Real estate taxes	28,284	26,901	81,771	76,001
Depreciation and amortization	42,475	38,490	121,826	119,868
Total operating expenses	137,864	130,539	399,835	384,517
Total operating income	48,538	56,007	132,367	142,712
Other income (expense):
Interest income	3,485	774	7,209	2,169
Interest expense	(20,658)	(16,890)	(58,774)	(52,109)
Loss on early extinguishment of debt	0	(2,157)	0	(2,157)
Loss from derivative financial instruments	0	0	0	(289)
Income before income taxes	31,365	37,734	80,802	90,326
Income tax expense	(2,135)	(2,245)	(3,330)	(4,333)
Net income	29,230	35,489	77,472	85,993
Private perpetual preferred unit distributions	(234)	(234)	(702)	(702)
Net income attributable to non-controlling interests	(12,654)	(16,449)	(34,009)	(39,916)
Net income attributable to common stockholders	$ 16,342	$ 18,806	$ 42,761	$ 45,375
Total weighted average shares:
Basic (in shares)	167,657	158,102	165,613	157,796
Diluted (in shares)	297,478	297,871	297,181	298,089
Earnings per share attributable to common stockholders:
Basic (in USD per share)	$ 0.10	$ 0.12	$ 0.26	$ 0.29
Diluted (in USD per share)	0.10	0.12	0.26	0.29
Dividends per share (in USD per share)	$ 0.105	$ 0.105	$ 0.315	$ 0.315