CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
REVENUES (Note 1)
Revenue	$ 200,492	$ 187,072	$ 401,694	$ 369,894
EXPENSES
Real estate taxes	17,926	17,813	36,565	34,959
Provision for bad debts (Note 1)	0	5,641	0	5,376
Ground leases (Notes 1 and 10)	2,114	1,586	4,086	3,147
General and administrative expenses	19,857	21,763	43,198	37,322
Leasing costs (Note 1)	2,650		4,407
Depreciation and amortization	68,252	64,006	134,387	126,721
Total expenses	149,335	143,376	299,328	271,763
OTHER (EXPENSES) INCOME
Interest income and other net investment gain (Note 11)	616	771	2,444	805
Interest expense (Note 4)	(11,727)	(12,712)	(22,970)	(26,210)
Gains on sales of depreciable operating properties (Note 2)	7,169	0	7,169	0
Total other (expenses) income	(3,942)	(11,941)	(13,357)	(25,405)
NET INCOME	47,215	31,755	89,009	72,726
Net income attributable to noncontrolling common units of the Operating Partnership	(871)	(566)	(1,571)	(1,317)
Net income attributable to noncontrolling interests in consolidated property partnerships	(4,150)	(3,640)	(8,341)	(7,614)
Total income attributable to noncontrolling interests	(5,021)	(4,206)	(9,912)	(8,931)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS (UNITHOLDERS)	$ 42,194	$ 27,549	$ 79,097	$ 63,795
Net income available to common stockholders per share – basic (in dollars per share)	$ 0.41	$ 0.27	$ 0.77	$ 0.63
Net income available to common stockholders per share – diluted (in dollars per share)	$ 0.41	$ 0.27	$ 0.77	$ 0.63
Weighted average common shares outstanding – basic (in shares)	100,972,355	99,691,700	100,937,069	99,220,577
Weighted average common shares outstanding – diluted (in shares)	101,809,541	100,150,856	101,618,953	99,687,682
Rental income [Member]
REVENUES (Note 1)
Revenue	$ 197,629	$ 164,515	$ 397,011	$ 327,386
Tenant reimbursements [Member]
REVENUES (Note 1)
Revenue	0	19,567	0	38,717
Other property income [Member]
REVENUES (Note 1)
Revenue	2,863	2,990	4,683	3,791
Property [Member]
EXPENSES
Property expenses (Note 1)	$ 38,536	$ 32,567	$ 76,685	$ 64,238