Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Adjustments to reconcile net income to net cash provided by operating activities
Net income (loss)	$ 58,321,000	$ 39,773,000	$ 31,522,000
Depreciation and amortization	158,389,000	125,159,000	86,589,000
Amortization of deferred financing costs	2,428,000	2,299,000	2,325,000
Amortization of lease inducements and above/below-market lease intangibles	4,659,000	5,083,000	3,906,000
Straight-line rental revenue/expense	(21,860,000)	(16,202,000)	(16,226,000)
Amortization of discount on unsecured senior notes	577,000	277,000	0
Amortization of above market assumed debt	(62,000)	(178,000)	(236,000)
Gain on sale of investment properties, net	(11,664,000)	(5,874,000)	0
Equity in income of unconsolidated entities	(114,000)	(183,000)	(115,000)
Distributions from unconsolidated entities	112,000	210,000	82,000
Change in fair value of derivatives	(6,000)	150,000	(240,000)
Provision for bad debts	304,000	123,000	2,310,000
Non-cash share compensation	8,681,000	6,695,000	5,672,000
Net change in fair value of contingent consideration	(50,000)	(472,000)	(840,000)
Impairment on investment properties	0	965,000	0
Change in operating assets and liabilities:
Tenant receivables	230,000	(2,988,000)	(10,058,000)
Other assets	(852,000)	(533,000)	(19,230,000)
Accounts payable	(7,137,000)	6,600,000	3,779,000
Accrued expenses and other liabilities	16,738,000	19,567,000	37,957,000
Net cash provided by operating activities	208,694,000	180,471,000	127,197,000
Cash Flows from Investing Activities:
Proceeds on sale of investment properties	217,222,000	20,397,000	0
Acquisition of investment properties, net	(243,001,000)	(1,268,442,000)	(1,240,438,000)
Acquisition of noncontrolling interests	0	(8,469,000)	(4,690,000)
Escrowed cash - acquisition deposits/earnest deposits	2,780,000	(1,280,000)	(1,157,000)
Capital expenditures on existing investment properties	(34,638,000)	(23,243,000)	(11,304,000)
Pay down of contingent consideration	0	(156,000)	(483,000)
Issuances of real estate loans receivable	(11,750,000)	(39,063,000)	(10,207,000)
Repayments of real estate loan receivable	15,928,000	4,711,000	11,336,000
Issuances of note receivable	(20,385,000)	0	0
Repayments of note receivable	0	16,423,000	4,118,000
Leasing commissions	(3,167,000)	(1,449,000)	(1,034,000)
Lease inducements	(172,000)	(2,067,000)	(8,957,000)
Net cash used in investing activities	(77,183,000)	(1,302,638,000)	(1,262,816,000)
Cash Flows from Financing Activities:
Net proceeds from sale of common shares	10,759,000	844,669,000	766,841,000
Proceeds from credit facility borrowings	422,000,000	927,000,000	1,181,000,000
Repayments on credit facility borrowings	(287,000,000)	(1,248,000,000)	(925,000,000)
Proceeds from issuance of senior unsecured notes	0	743,060,000	225,000,000
Proceeds from issuance of mortgage debt	0	61,000,000	39,500,000
Principal payments on mortgage debt	(78,018,000)	(41,503,000)	(10,232,000)
Debt issuance costs	(4,540,000)	(1,589,000)	(4,816,000)
Dividends paid - shareholders	(168,060,000)	(143,108,000)	(104,908,000)
Distributions to noncontrolling interest - Operating Partnership	(4,808,000)	(4,388,000)	(3,162,000)
Preferred distributions paid - OP Unit holders	(911,000)	(600,000)	(1,508,000)
Contributions to noncontrolling interests	0	47,000	0
Distributions to noncontrolling interests - partially owned properties	(547,000)	(748,000)	(543,000)
Payments of employee taxes for withheld stock-based compensation shares	(1,749,000)	(2,590,000)	(778,000)
Purchases of Series A Preferred Units	0	(19,961,000)	(9,756,000)
Purchases of OP Units	(2,203,000)	(3,886,000)	(3,671,000)
Net cash (used in) provided by financing activities	(115,077,000)	1,109,403,000	1,147,967,000
Net increase (decrease) in cash and cash equivalents	16,434,000	(12,764,000)	12,348,000
Cash and cash equivalents, beginning of period	2,727,000	15,491,000	3,143,000
Cash and cash equivalents, end of period	19,161,000	2,727,000	15,491,000
Supplemental cash flow information:
Supplemental disclosure of cash flow information - interest paid during the year	58,705,000	38,781,000	17,151,000
Supplemental disclosure of noncash activity - change in fair value of interest rate swap agreements and redeemable equity - property	481,000	244,000	13,708,000
Supplemental disclosure of noncash activity - assumed debt	0	43,989,000	0
Supplemental disclosure of noncash activity - issuance of OP Units and Series A Preferred Units in connection with acquisitions	22,651,000	44,978,000	6,769,000
Supplemental disclosure of noncash activity - contingent consideration	0	765,000	156,000
Operating Partnership
Adjustments to reconcile net income to net cash provided by operating activities
Net income (loss)	58,321,000	39,773,000	31,522,000
Depreciation and amortization	158,389,000	125,159,000	86,589,000
Amortization of deferred financing costs	2,428,000	2,299,000	2,325,000
Amortization of lease inducements and above/below-market lease intangibles	4,659,000	5,083,000	3,906,000
Straight-line rental revenue/expense	(21,860,000)	(16,202,000)	(16,226,000)
Amortization of discount on unsecured senior notes	577,000	277,000	0
Amortization of above market assumed debt	(62,000)	(178,000)	(236,000)
Gain on sale of investment properties, net	(11,664,000)	(5,874,000)	0
Equity in income of unconsolidated entities	(114,000)	(183,000)	(115,000)
Distributions from unconsolidated entities	112,000	210,000	82,000
Change in fair value of derivatives	(6,000)	150,000	(240,000)
Provision for bad debts	304,000	123,000	2,310,000
Non-cash share compensation	8,681,000	6,695,000	5,672,000
Net change in fair value of contingent consideration	(50,000)	(472,000)	(840,000)
Impairment on investment properties	0	965,000	0
Change in operating assets and liabilities:
Tenant receivables	230,000	(2,988,000)	(10,058,000)
Other assets	(852,000)	(533,000)	(19,230,000)
Accounts payable	(7,137,000)	6,600,000	3,779,000
Accrued expenses and other liabilities	16,738,000	19,567,000	37,957,000
Net cash provided by operating activities	208,694,000	180,471,000	127,197,000
Cash Flows from Investing Activities:
Proceeds on sale of investment properties	217,222,000	20,397,000	0
Acquisition of investment properties, net	(243,001,000)	(1,268,442,000)	(1,240,438,000)
Acquisition of noncontrolling interests	0	(8,469,000)	(4,690,000)
Escrowed cash - acquisition deposits/earnest deposits	2,780,000	(1,280,000)	(1,157,000)
Capital expenditures on existing investment properties	(34,638,000)	(23,243,000)	(11,304,000)
Pay down of contingent consideration	0	(156,000)	(483,000)
Issuances of real estate loans receivable	(11,750,000)	(39,063,000)	(10,207,000)
Repayments of real estate loan receivable	15,928,000	4,711,000	11,336,000
Issuances of note receivable	(20,385,000)	0	0
Repayments of note receivable	0	16,423,000	4,118,000
Leasing commissions	(3,167,000)	(1,449,000)	(1,034,000)
Lease inducements	(172,000)	(2,067,000)	(8,957,000)
Net cash used in investing activities	(77,183,000)	(1,302,638,000)	(1,262,816,000)
Cash Flows from Financing Activities:
Net proceeds from sale of common shares	10,759,000	844,669,000	766,841,000
Proceeds from credit facility borrowings	422,000,000	927,000,000	1,181,000,000
Repayments on credit facility borrowings	(287,000,000)	(1,248,000,000)	(925,000,000)
Proceeds from issuance of senior unsecured notes	0	743,060,000	225,000,000
Proceeds from issuance of mortgage debt	0	61,000,000	39,500,000
Principal payments on mortgage debt	(78,018,000)	(41,503,000)	(10,232,000)
Debt issuance costs	(4,540,000)	(1,589,000)	(4,816,000)
Dividends paid - shareholders	(168,060,000)	(143,108,000)	(104,908,000)
Distributions to noncontrolling interest - Operating Partnership	(4,808,000)	(4,388,000)	(3,162,000)
Preferred distributions paid - OP Unit holders	(911,000)	(600,000)	(1,508,000)
Contributions to noncontrolling interests	0	47,000	0
Distributions to noncontrolling interests - partially owned properties	(547,000)	(748,000)	(543,000)
Payments of employee taxes for withheld stock-based compensation shares	(1,749,000)	(2,590,000)	(778,000)
Purchases of Series A Preferred Units	0	(19,961,000)	(9,756,000)
Purchases of OP Units	(2,203,000)	(3,886,000)	(3,671,000)
Net cash (used in) provided by financing activities	(115,077,000)	1,109,403,000	1,147,967,000
Net increase (decrease) in cash and cash equivalents	16,434,000	(12,764,000)	12,348,000
Cash and cash equivalents, beginning of period	2,727,000	15,491,000	3,143,000
Cash and cash equivalents, end of period	19,161,000	2,727,000	15,491,000
Supplemental cash flow information:
Supplemental disclosure of cash flow information - interest paid during the year	58,705,000	38,781,000	17,151,000
Supplemental disclosure of noncash activity - change in fair value of interest rate swap agreements and redeemable equity - property	481,000	244,000	13,708,000
Supplemental disclosure of noncash activity - assumed debt	0	43,989,000	0
Supplemental disclosure of noncash activity - issuance of OP Units and Series A Preferred Units in connection with acquisitions	22,651,000	44,978,000	6,769,000
Supplemental disclosure of noncash activity - contingent consideration	$ 0	$ 765,000	$ 156,000