Consolidated Statements of Income - USD ($)		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues:
Rental revenues										$ 259,673,000	$ 186,301,000	$ 103,974,000
Expense recoveries										75,425,000	45,875,000	21,587,000
Interest income on real estate loans and other										8,486,000	8,858,000	3,880,000
Total revenues		$ 97,320,000	$ 92,999,000	$ 76,599,000	$ 76,666,000	$ 73,674,000	$ 70,010,000	$ 53,216,000	$ 44,134,000	343,584,000	241,034,000	129,441,000
Expenses:
Interest expense										47,008,000	23,864,000	10,636,000
General and administrative										22,957,000	18,397,000	14,908,000
Operating expenses										97,035,000	65,999,000	31,026,000
Depreciation and amortization										125,159,000	86,589,000	45,471,000
Acquisition expenses										16,744,000	14,778,000	14,893,000
Impairment loss										965,000	0	0
Total expenses										309,868,000	209,627,000	116,934,000
Income before equity in income of unconsolidated entities and gain on sale of investment properties:		9,523,000	12,511,000	4,994,000	6,688,000	8,590,000	10,267,000	7,158,000	5,392,000	33,716,000	31,407,000	12,507,000
Equity in income of unconsolidated entities										183,000	115,000	104,000
Gain on sale of investment properties										5,874,000	0	130,000
Net income		10,187,000	12,539,000	10,331,000	6,716,000	8,620,000	10,294,000	7,184,000	5,424,000	39,773,000	31,522,000	12,741,000
Net income attributable to noncontrolling interests:
Operating Partnership										(1,136,000)	(825,000)	(576,000)
Partially owned properties	[1]									(491,000)	(716,000)	(377,000)
Net income attributable to controlling interest										38,146,000	29,981,000	11,788,000
Preferred distributions										(731,000)	(1,857,000)	(1,189,000)
Net income attributable to common shareholders		$ 9,536,000	$ 12,018,000	$ 9,670,000	$ 6,191,000	$ 7,825,000	$ 9,427,000	$ 6,486,000	$ 4,386,000	$ 37,415,000	$ 28,124,000	$ 10,599,000
Net income per share:
Earnings per share - basic (in dollars per share)		$ 0.05	$ 0.07	$ 0.06	$ 0.04	$ 0.06	$ 0.07	$ 0.05	$ 0.04	$ 0.23	$ 0.22	$ 0.15
Earnings per share - diluted (in dollars per share)		$ 0.05	$ 0.07	$ 0.06	$ 0.04	$ 0.06	$ 0.07	$ 0.05	$ 0.04	$ 0.23	$ 0.22	$ 0.15
Weighted average common shares:
Weighted average common shares - basic (in shares)		179,683,948	177,847,424	155,366,080	138,986,629	135,581,976	134,608,396	131,481,329	102,704,008	163,123,109	126,143,114	72,750,724
Weighted average common shares - diluted (in shares)		185,273,236	183,298,145	161,012,360	142,605,930	139,602,349	138,880,787	135,944,722	107,148,380	168,231,299	130,466,893	76,792,073
Dividends and distributions declared per common share and OP unit (in dollars per share)										$ 0.915	$ 0.900	$ 0.900
Earnings per unit:
Net income (loss) attributable to redeemable noncontrolling interest										$ 300,000	$ 100,000	$ 0
Operating Partnership
Revenues:
Rental revenues										259,673,000	186,301,000	103,974,000
Expense recoveries										75,425,000	45,875,000	21,587,000
Interest income on real estate loans and other										8,486,000	8,858,000	3,880,000
Total revenues		$ 97,320,000	$ 92,999,000	$ 76,599,000	$ 76,666,000	$ 73,674,000	$ 70,010,000	$ 53,216,000	$ 44,134,000	343,584,000	241,034,000	129,441,000
Expenses:
Interest expense										47,008,000	23,864,000	10,636,000
General and administrative										22,957,000	18,397,000	14,908,000
Operating expenses										97,035,000	65,999,000	31,026,000
Depreciation and amortization										125,159,000	86,589,000	45,471,000
Acquisition expenses										16,744,000	14,778,000	14,893,000
Impairment loss										965,000	0
Total expenses										309,868,000	209,627,000	116,934,000
Income before equity in income of unconsolidated entities and gain on sale of investment properties:		9,523,000	12,511,000	4,994,000	6,688,000	8,590,000	10,267,000	7,158,000	5,392,000	33,716,000	31,407,000	12,507,000
Equity in income of unconsolidated entities										183,000	115,000	104,000
Gain on sale of investment properties										5,874,000	0	130,000
Net income		10,187,000	12,539,000	10,331,000	6,716,000	8,620,000	10,294,000	7,184,000	5,424,000	39,773,000	31,522,000	12,741,000
Net income attributable to noncontrolling interests:
Partially owned properties										(491,000)	(716,000)	(377,000)	[1]
Net income attributable to controlling interest										39,282,000	30,806,000	12,364,000
Preferred distributions										(731,000)	(1,857,000)	(1,189,000)
Net income attributable to common shareholders		$ 9,849,000	$ 12,380,000	$ 9,984,000	$ 6,338,000	$ 8,021,000	$ 9,682,000	$ 6,687,000	$ 4,559,000	$ 38,551,000	$ 28,949,000	$ 11,175,000
Net income per share:
Earnings per share - basic (in dollars per share)		$ 0.05	$ 0.07	$ 0.06	$ 0.04	$ 0.06	$ 0.07	$ 0.05	$ 0.04
Earnings per share - diluted (in dollars per share)		$ 0.05	$ 0.07	$ 0.06	$ 0.04	$ 0.06	$ 0.07	$ 0.05	$ 0.04
Earnings per unit:
Earnings per unit - basic (in dollars per share)										$ 0.23	$ 0.22	$ 0.15
Earnings per unit - diluted (in dollars per share)										$ 0.23	$ 0.22	$ 0.15
Weighted average common units - basic (in shares)		185,048,580	183,227,405	160,765,345	142,172,746	139,018,183	138,227,384	135,351,672	106,550,467	167,963,076	129,835,209	76,459,218
Weighted average common units - diluted (in shares)		185,273,236	183,298,145		142,605,930		138,880,787	135,944,722	107,148,380	168,231,299	130,466,893	76,792,073
Distributions declared per common OP Unit (in dollars per share)										$ 0.915	$ 0.900	$ 0.900
Net income (loss) attributable to redeemable noncontrolling interest										$ 300,000	$ 100,000	$ 0

[1] adjustment of $0.3 million and $0.1 million was required for net income attributable to redeemable noncontrolling interests for the year ended December 31, 2017 and December 31, 2016, respectively. No such adjustment was required for the year ended December 31, 2015.