Consolidated Statements of Cash Flows - USD ($)	3 Months Ended			6 Months Ended			9 Months Ended			12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net income	$ 5,424,000	$ (448,000)								$ 31,522,000	$ 12,741,000	$ (4,418,000)
Adjustments to reconcile net income (loss) to net cash provided by operating activities
Depreciation and amortization										86,589,000	45,471,000	16,731,000
Amortization of deferred financing costs										2,325,000	1,373,000	1,097,000
Amortization of lease inducements and above/below market lease intangibles										3,906,000	2,577,000	571,000
Straight-line rental revenue/expense										(16,226,000)	(9,000,000)	(4,366,000)
Amortization of above market assumed debt										(236,000)	(173,000)	0
Gain on sale of investment properties			$ 0							0	(130,000)	(32,000)
Equity in income of unconsolidated entities										(115,000)	(104,000)	(95,000)
Distribution from unconsolidated entities										82,000	106,000	71,000
Change in fair value of derivatives										(240,000)	(166,000)	(161,000)
Provision for bad debts										2,310,000	69,000	9,000
Non-cash share compensation										4,894,000	3,798,000	2,422,000
Ziegler shared service amendment payment										0	0	1,800,000
Write-off of contingent consideration										(840,000)	0	0
Impairment loss										0	0	1,750,000
Change in operating assets and liabilities:
Tenant receivables										(10,058,000)	(2,836,000)	(986,000)
Other assets										(20,387,000)	(630,000)	(3,518,000)
Accounts payable, trade										3,779,000	(56,000)	(136,000)
Accrued expenses and other liabilities										37,474,000	8,312,000	2,556,000
Net cash provided by operating activities										124,779,000	61,352,000	13,295,000
Cash Flows from Investing Activities:
Proceeds on sales of investment properties										0	3,039,000	235,000
Acquisition of investment properties, net										(1,245,128,000)	(752,807,000)	(501,127,000)
Capital expenditures on existing investment properties										(11,304,000)	(4,988,000)	(900,000)
Payments for real estate loans receivable										(10,207,000)	(22,359,000)	(15,386,000)
Pay down of contingent consideration										0	(999,000)	0
Repayment of real estate loan receivable										(11,336,000)	0	0
Note receivable										0	(20,545,000)	0
Repayment of note receivable										4,118,000	0	0
Leasing commissions										(1,034,000)	(579,000)	(100,000)
Lease inducements										(8,957,000)	(2,478,000)	(1,532,000)
Net cash used in investing activities										(1,261,176,000)	(801,716,000)	(518,810,000)
Cash Flows from Financing Activities:
Net proceeds from sale of common shares										766,841,000	545,117,000	350,384,000
Proceeds from credit facility borrowings										1,181,000,000	620,000,000	395,200,000
Payment on credit facility borrowings										(925,000,000)	(363,000,000)	(257,200,000)
Proceeds from issuance of mortgage debt										39,500,000	0	26,550,000
Proceeds from issuance of senior unsecured notes										225,000,000	0	0
Principal payments on mortgage debt										(10,232,000)	(2,022,000)	(6,549,000)
Debt issuance costs										(4,816,000)	(3,105,000)	(3,887,000)
Dividends paid - shareholders										(104,908,000)	(63,720,000)	(28,104,000)
Distributions to noncontrolling interest - Operating Partnership										(3,162,000)	(3,216,000)	(3,382,000)
Preferred distributions paid - OP Unit holder										(1,508,000)	(563,000)	0
Distributions to noncontrolling interest - partially owned properties										(543,000)	(213,000)	(185,000)
Purchase of Series A Preferred Units										(9,756,000)	0	0
Purchase of OP Units										(3,671,000)	(1,088,000)	(7,546,000)
Common shares repurchased and retired										0	(606,000)	(321,000)
Net cash provided by financing activities										1,148,745,000	727,584,000	464,960,000
Net increase (decrease) in cash and cash equivalents										12,348,000	(12,780,000)	(40,555,000)
Cash and cash equivalents, beginning of period	3,143,000	15,923,000	56,478,000	$ 3,143,000	$ 15,923,000	$ 56,478,000	$ 3,143,000	$ 15,923,000	$ 56,478,000	3,143,000	15,923,000	56,478,000
Cash and cash equivalents, end of period										15,491,000	3,143,000	15,923,000
Supplemental cash flow information:
Supplemental disclosure of cash flow information - interest paid during the year										17,151,000	9,550,000	5,606,000
Change in fair value of interest rate cap agreements										13,708,000	0	0
Noncash investing and financing activities:
Change in fair value of interest rate swap agreements										13,708,000	0	0
Supplemental disclosure of noncash activity - assumed debt										0	18,690,000	15,283,000
Supplemental disclosure of noncash activity - issuance of OP Units and Series A Preferred Units in connection with acquisitions										23,848,000	10,973,000	28,589,000
Supplemental disclosure of noncash activity - issuance of OP Units and Series A Preferred Units in connection with acquisitions										6,769,000	40,376,000	28,589,000
Supplemental disclosure of noncash activity - contingent consideration										156,000	2,718,000	840,000
Operating Partnership
Net income	5,424,000	(448,000)	(3,558,000)	12,608,000	2,849,000	(4,158,000)	22,902,000	6,832,000	(6,409,000)	31,522,000	12,741,000	(4,418,000)
Adjustments to reconcile net income (loss) to net cash provided by operating activities
Depreciation and amortization	16,010,000	8,240,000	2,416,000	35,809,000	18,591,000	6,152,000	59,778,000	31,067,000	10,565,000	86,589,000	45,471,000	16,731,000
Amortization of deferred financing costs	448,000	293,000	148,000	947,000	594,000	352,000	1,796,000	953,000	626,000	2,325,000	1,373,000	1,097,000
Accelerated amortization of deferred financing costs								0	141,000	0	0	0
Amortization of lease inducements and above/below market lease intangibles	962,000	302,000	81,000	1,989,000	838,000	186,000	2,994,000	1,559,000	331,000	3,906,000	2,577,000	571,000
Straight-line rental revenue/expense	(3,185,000)	(2,012,000)	(652,000)	(7,204,000)	(3,889,000)	(1,585,000)	(12,156,000)	(6,262,000)	(2,785,000)	(16,226,000)	(9,000,000)	(4,366,000)
Amortization of above market assumed debt	(59,000)	(10,000)	0	(118,000)	(55,000)	0	(177,000)	(114,000)	0	(236,000)	(173,000)	0
Gain on sale of investment properties	0	15,000	0	0	15,000	0	0	(130,000)	(34,000)	0	(130,000)	(32,000)
Equity in income of unconsolidated entities	(32,000)	(26,000)	(17,000)	(58,000)	(52,000)	(43,000)	(85,000)	(78,000)	(69,000)	(115,000)	(104,000)	(95,000)
Distribution from unconsolidated entities	27,000	26,000	0	27,000	53,000	45,000	82,000	79,000	45,000	82,000	106,000	71,000
Change in fair value of derivatives	(40,000)	(13,000)	(41,000)	(67,000)	(154,000)	(72,000)	(67,000)	(116,000)	(138,000)	(240,000)	(166,000)	(161,000)
Provision for bad debts	30,000	0	6,000	104,000	0	6,000	152,000	26,000	5,000	2,310,000	69,000	9,000
Non-cash share compensation	1,185,000	867,000	356,000	2,599,000	1,944,000	860,000	3,497,000	2,929,000	1,681,000	4,894,000	3,798,000	2,422,000
Ziegler shared service amendment payment								0	1,800,000	0	0	1,800,000
Write-off of contingent consideration							(840,000)	0		(840,000)	0	0
Impairment loss								0	250,000	0	0	1,750,000
Change in operating assets and liabilities:
Tenant receivables	(3,665,000)	(1,022,000)	(591,000)	(1,001,000)	(1,453,000)	(50,000)	(7,543,000)	(2,448,000)	(521,000)	(10,058,000)	(2,836,000)	(986,000)
Other assets	(1,995,000)	(580,000)	6,000	(3,081,000)	(1,231,000)	402,000	(6,320,000)	(1,268,000)	(1,285,000)	(20,387,000)	(630,000)	(3,518,000)
Accounts payable to related parties											0	0
Accounts payable, trade	1,015,000	(252,000)	(114,000)	1,079,000	397,000	(138,000)	1,578,000	693,000	(203,000)	3,779,000	(56,000)	(136,000)
Accrued expenses and other liabilities	4,023,000	4,345,000	1,580,000	15,908,000	4,013,000	1,954,000	23,832,000	7,929,000	3,445,000	37,474,000	8,312,000	2,556,000
Net cash provided by operating activities	20,148,000	9,725,000	(380,000)	59,541,000	22,460,000	3,911,000	89,423,000	41,651,000	7,445,000	124,779,000	61,352,000	13,295,000
Cash Flows from Investing Activities:
Proceeds on sales of investment properties	0	1,550,000	0	0	1,550,000	0	0	3,039,000	235,000	0	3,039,000	235,000
Acquisition of investment properties, net	(197,876,000)	(205,278,000)	(138,779,000)	(872,497,000)	(336,128,000)	(208,118,000)	(1,044,601,000)	(629,888,000)	(404,715,000)	(1,245,128,000)	(752,807,000)	(501,127,000)
Capital expenditures on existing investment properties	(1,820,000)	(1,028,000)	0	(6,980,000)	(1,815,000)	(87,000)	(8,665,000)	(3,974,000)	(551,000)	(11,304,000)	(4,988,000)	(900,000)
Payments for real estate loans receivable	(500,000)	(4,123,000)	(6,836,000)	(3,478,000)	(9,000,000)	(6,836,000)	(8,153,000)	(12,404,000)	(6,836,000)
Pay down of contingent consideration										(10,207,000)	(999,000)	0
Proceeds from (payments for) real estate loans receivable										11,336,000	(22,359,000)	(15,386,000)
Repayment of real estate loan receivable	(4,500,000)	0		(4,500,000)	0		(4,500,000)	0		(4,118,000)	0	0
Note receivable				0	(4,123,000)	0	0	(4,123,000)	0	0	(20,545,000)	0
Repayment of note receivable				4,118,000	0		4,118,000	0
Leasing commissions	(58,000)	(35,000)	(5,000)	(116,000)	(63,000)	(5,000)	(707,000)	(278,000)	(5,000)	(1,034,000)	(579,000)	(100,000)
Lease inducements	(1,284,000)	(462,000)	0	(4,870,000)	(2,445,000)	(1,500,000)	(4,870,000)	(2,478,000)	(1,532,000)	(8,957,000)	(2,478,000)	(1,532,000)
Net cash used in investing activities	(197,038,000)	(209,376,000)	(145,620,000)	(879,323,000)	(352,024,000)	(216,546,000)	(1,058,378,000)	(650,106,000)	(413,404,000)	(1,261,176,000)	(801,716,000)	(518,810,000)
Cash Flows from Financing Activities:
Net proceeds from sale of common shares	321,238,000	301,772,000	(57,000)	764,205,000	318,041,000	149,917,000	764,292,000	318,170,000	295,610,000	766,841,000	545,117,000	350,384,000
Formation transactions										0	0	0
Proceeds from credit facility borrowings	150,000,000	73,000,000	80,000,000	528,000,000	191,000,000	113,200,000	921,000,000	473,000,000	286,200,000	1,181,000,000	620,000,000	395,200,000
Payment on credit facility borrowings	(424,000,000)	(138,000,000)	0	(545,000,000)	(138,000,000)	(113,200,000)	(860,000,000)	(138,000,000)	(216,200,000)	(925,000,000)	(363,000,000)	(257,200,000)
Proceeds from issuance of mortgage debt	21,500,000	0	26,550,000	21,500,000	0	26,550,000	21,500,000	0	26,550,000	39,500,000	0	26,550,000
Proceeds from issuance of senior unsecured notes	150,000,000	0		150,000,000	0		225,000,000	0		225,000,000	0	0
Principal payments on mortgage debt	(541,000)	(466,000)	(384,000)	(1,089,000)	(966,000)	(803,000)	(1,646,000)	(1,486,000)	(1,234,000)	(10,232,000)	(2,022,000)	(6,549,000)
Debt issuance costs	(808,000)	(24,000)	(761,000)	(4,313,000)	(144,000)	(1,331,000)	(4,693,000)	(3,029,000)	(3,848,000)	(4,816,000)	(3,105,000)	(3,887,000)
Dividends paid - shareholders	(19,666,000)	(15,792,000)	(4,848,000)	(44,151,000)	(31,613,000)	(9,716,000)	(74,515,000)	(47,665,000)	(17,443,000)	(104,908,000)	(63,720,000)	(28,104,000)
Distributions to noncontrolling interest - Operating Partnership	(809,000)	(714,000)	(832,000)	(1,616,000)	(1,523,000)	(1,664,000)	(2,410,000)	(2,374,000)	(2,665,000)	(3,162,000)	(3,216,000)	(3,382,000)
Preferred distributions paid - OP Unit holder	(204,000)	0		(704,000)	(238,000)	0	(1,115,000)	(360,000)	0	(1,508,000)	0	0
Distributions to noncontrolling interest - partially owned properties	(57,000)	(69,000)	(54,000)	(363,000)	(114,000)	(99,000)	(450,000)	(158,000)	(143,000)	(543,000)	(213,000)	(185,000)
Purchase of Series A Preferred Units				(9,756,000)	0		(9,756,000)	0		(9,756,000)	(563,000)	0
Purchase of OP Units	0	(205,000)	0	(2,129,000)	(253,000)	0	(2,999,000)	(253,000)	0	(3,671,000)	(1,088,000)	(7,546,000)
Common shares repurchased and retired							0	(595,000)	(321,000)	0	(606,000)	(321,000)
Net cash provided by financing activities	196,653,000	219,502,000	99,614,000	854,584,000	336,190,000	162,854,000	974,208,000	597,250,000	366,506,000	1,148,745,000	727,584,000	464,960,000
Net increase (decrease) in cash and cash equivalents	19,763,000	19,851,000	(46,386,000)	34,802,000	6,626,000	(49,781,000)	5,253,000	(11,205,000)	(39,453,000)	12,348,000	(12,780,000)	(40,555,000)
Cash and cash equivalents, beginning of period	3,143,000	15,923,000	56,478,000	3,143,000	15,923,000	56,478,000	3,143,000	15,923,000	56,478,000	3,143,000	15,923,000	56,478,000
Cash and cash equivalents, end of period	22,906,000	35,774,000	10,092,000	37,945,000	22,549,000	6,697,000	8,396,000	4,718,000	17,025,000	15,491,000	3,143,000	15,923,000
Supplemental cash flow information:
Supplemental disclosure of cash flow information - interest paid during the year	2,181,000	1,402,000	1,025,000	4,300,000	3,332,000	2,607,000	12,074,000	6,010,000	4,113,000	17,151,000	9,550,000	5,606,000
Change in fair value of interest rate cap agreements							652,000			13,708,000	0	0
Noncash investing and financing activities:
Change in fair value of interest rate swap agreements							652,000	0		13,708,000	0	0
Supplemental disclosure of noncash activity - assumed debt	0	6,323,000	10,800,000	0	18,690,000	10,395,000	0	18,690,000	15,283,000	0	18,690,000	15,283,000
Supplemental disclosure of noncash activity - issuance of OP Units and Series A Preferred Units in connection with acquisitions	2,869,000	17,017,000
Supplemental disclosure of noncash activity - issuance of OP Units and Series A Preferred Units in connection with acquisitions		17,017,000	0		20,438,000	3,135,000		20,677,000	28,589,000
Supplemental disclosure of noncash activity - issuance of OP Units and Series A Preferred Units in connection with acquisitions				6,869,000	20,438,000		6,769,000	20,677,000		6,769,000	40,376,000	28,589,000
Supplemental disclosure of noncash activity - contingent consideration	$ 0	$ 1,482,000	$ 0	$ 156,000	$ 1,482,000	$ 0	$ 156,000	$ 550,000	$ 840,000	$ 156,000	$ 2,718,000	$ 840,000