STAG Industrial (STAG) 10-Q 1 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 31, 2018
Document and Entity Information
Entity Registrant Name	STAG Industrial, Inc.
Entity Central Index Key	1,479,094
Document Period End Date	Sep. 30, 2018
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		108,893,286
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Document Type	10-Q
Amendment Flag	false

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Rental Property:
Land	$ 355,590	$ 321,560
Buildings and improvements, net of accumulated depreciation of $301,787 and $249,057, respectively	2,202,755	1,932,764
Deferred leasing intangibles, net of accumulated amortization of $237,892 and $280,642, respectively	327,734	313,253
Total rental property, net	2,886,079	2,567,577
Cash and cash equivalents	6,024	24,562
Restricted cash	5,231	3,567
Tenant accounts receivable, net	39,170	33,602
Prepaid expenses and other assets	35,122	25,364
Interest rate swaps	17,649	6,079
Assets held for sale, net	0	19,916
Total assets	2,989,275	2,680,667
Liabilities:
Unsecured credit facility	95,000	271,000
Unsecured term loans, net	596,085	446,265
Unsecured notes, net	572,389	398,234
Mortgage notes, net	56,993	58,282
Accounts payable, accrued expenses and other liabilities	53,445	43,216
Interest rate swaps	0	1,217
Tenant prepaid rent and security deposits	19,328	19,045
Dividends and distributions payable	14,530	11,880
Deferred leasing intangibles, net of accumulated amortization of $13,043 and $13,555, respectively	20,708	21,221
Total liabilities	1,428,478	1,270,360
Commitments and contingencies (Note 10)
Preferred stock, par value $0.01 per share, 15,000,000 shares authorized,
Common stock, par value $0.01 per share, 150,000,000 shares authorized, 107,825,791 and 97,012,543 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively	1,078	970
Additional paid-in capital	2,003,983	1,725,825
Cumulative dividends in excess of earnings	(589,785)	(516,691)
Accumulated other comprehensive income	16,485	3,936
Total stockholders’ equity	1,506,761	1,359,040
Noncontrolling interest	54,036	51,267
Total equity	1,560,797	1,410,307
Total liabilities and equity	2,989,275	2,680,667
Series B Preferred Stock
Preferred stock, par value $0.01 per share, 15,000,000 shares authorized,
Preferred stock	0	70,000
Series C Preferred Stock
Preferred stock, par value $0.01 per share, 15,000,000 shares authorized,
Preferred stock	$ 75,000	$ 75,000

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Building and Improvements	$ 301,787	$ 249,057
Deferred leasing intangibles assets, accumulated amortization	237,892	280,642
Deferred leasing intangibles liabilities, accumulated amortization	$ 13,043	$ 13,555
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	15,000,000	15,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Common Stock, shares, issued	104,238,166	97,012,543
Common stock, shares outstanding	104,238,166	97,012,543
Series B Preferred Stock
Preferred stock, shares issued	0	2,800,000
Preferred stock, shares outstanding	0	2,800,000
Preferred stock, liquidation preference (in dollars per share)	$ 0	$ 25
Series C Preferred Stock
Preferred stock, shares issued	3,000,000	3,000,000
Preferred stock, shares outstanding	3,000,000	3,000,000
Preferred stock, liquidation preference (in dollars per share)	$ 25	$ 25

Consolidated Statements of Oper

Consolidated Statements of Operations - 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 [Abstract]
Rental income	$ 75,159	$ 65,673	$ 217,227	$ 186,621
Tenant recoveries	13,518	12,366	39,443	32,952
Other income	269	105	1,033	244
Total revenue	88,946	78,144	257,703	219,817
Expenses
Property	17,112	15,401	50,735	42,312
General and administrative	8,911	8,380	25,637	25,090
Property acquisition costs	0	1,386	0	4,684
Depreciation and amortization	44,355	38,186	125,221	110,286
Loss on impairments	0	0	2,934	0
Loss on involuntary conversion	0	0	0	330
Other expenses	223	58	864	1,502
Total expenses	70,601	63,411	205,391	184,204
Other income (expense)
Interest and other income	3	2	16	10
Interest expense	(12,698)	(10,446)	(35,602)	(31,557)
Loss on extinguishment of debt	(13)	(13)	(13)	(15)
Gain on the sales of rental property, net	3,239	17,563	32,276	19,225
Total other income (expense)	(9,469)	7,106	(3,323)	(12,337)
Net income	8,876	21,839	48,989	23,276
Less: income attributable to noncontrolling interest after preferred stock dividends	281	828	1,589	673
Net income attributable to STAG Industrial, Inc.	8,595	21,011	47,400	22,603
Less: preferred stock dividends	1,289	2,449	6,315	7,345
Less: redemption of preferred stock	0	0	2,661	0
Less: amount allocated to participating securities	69	84	209	250
Net income attributable to common stockholders	$ 7,237	$ 18,478	$ 38,215	$ 15,008
Weighted average common shares outstanding — basic	105,783	92,787	101,095	87,632
Weighted average common shares outstanding — diluted	106,333	93,435	101,495	88,238
Net income per share — basic and diluted
Net income per share attributable to common stockholders — basic	$ 0.07	$ 0.20	$ 0.38	$ 0.17
Net income per share attributable to common stockholders — diluted	$ 0.07	$ 0.20	$ 0.38	$ 0.17

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 8,876	$ 21,839	$ 48,989	$ 23,276
Other comprehensive income:
Income on interest rate swaps	2,060	598	12,811	300
Other comprehensive income	2,060	598	12,811	300
Comprehensive income	10,936	22,437	61,800	23,576
Income attributable to noncontrolling interest after preferred stock dividends	(281)	(828)	(1,589)	(673)
Other comprehensive income attributable to noncontrolling interest	(76)	(26)	(509)	(13)
Comprehensive income attributable to STAG Industrial, Inc.	$ 10,579	$ 21,583	$ 59,702	$ 22,890

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-in Capital	Common Stock Dividends in excess of Earnings	Accumulated Other Comprehensive Income (Loss)	Total Stockholders' Equity	Noncontrolling Interest - Unit holders in Operating Partnership
Balance at Dec. 31, 2016	$ 1,066,926	$ 145,000	$ 804	$ 1,293,706	$ (410,978)	$ (1,496)	$ 1,027,036	$ 39,890
Balance (in shares) at Dec. 31, 2016			80,352,304
Increase (Decrease) in Stockholders' Equity
Proceeds from sales of common stock	339,624		$ 132	339,492			339,624
Proceeds from sales of common stock (in shares)			13,165,996
Offering costs	(4,746)			(4,746)			(4,746)
Dividends, Preferred Stock		0
Dividends, Common Stock					100,509
Dividends							100,509
Dividends and Distributions, Net	105,441
Distribution Made to Limited Partner, Cash Distributions Declared								4,932
Non-cash compensation activity, net	6,226			2,911			2,717	3,509
Non-cash compensation activity (in shares)			43,492
Non-cash compensation activity (in excess of earnings)			$ 0		(194)
Redemption of common units to common stock			$ 3	3,314			3,317	(3,317)
Redemption of common units to common stock (in shares)			300,991
Issuance of units	18,558							18,558
Rebalancing of noncontrolling interest				3,632			3,632	(3,632)
Other comprehensive income	300					287	287	13
Net income	23,276	0			22,603		22,603	673
Balance at Sep. 30, 2017	1,344,723	145,000	$ 939	1,638,309	(489,078)	(1,209)	1,293,961	50,762
Balance (in shares) at Sep. 30, 2017			93,862,783
Balance at Dec. 31, 2016	1,066,926	145,000	$ 804	1,293,706	(410,978)	(1,496)	1,027,036	$ 39,890
Balance (in shares) at Dec. 31, 2016			80,352,304
Increase (Decrease) in Stockholders' Equity
Redemption of common units to common stock (in shares)								0
Balance at Dec. 31, 2017	1,410,307	145,000	$ 970	1,725,825	(516,691)	3,936	1,359,040	$ 51,267
Balance (in shares) at Dec. 31, 2017			97,012,543
Increase (Decrease) in Stockholders' Equity
Cash flow hedging instruments cumulative effect adjustment (Note 2)					(258)	247	(11)	11
Proceeds from sales of common stock	276,457		$ 104	276,353			276,457
Proceeds from sales of common stock (in shares)			10,387,962
Redemption of preferred stock	(70,017)	(70,000)		(5,141)	(5,158)		(70,017)	0
Offering costs	(3,129)			(3,129)			(3,129)
Dividends, Preferred Stock		0
Dividends, Common Stock					114,541
Dividends							114,541
Dividends and Distributions, Net	119,794
Distribution Made to Limited Partner, Cash Distributions Declared								5,253
Non-cash compensation activity, net	5,173			1,829			1,293	3,880
Non-cash compensation activity (in shares)			73,231
Non-cash compensation activity (in excess of earnings)			$ (1)		(537)
Redemption of common units to common stock			$ 3	4,398			4,401	$ (4,401)
Redemption of common units to common stock (in shares)			352,055					0
Rebalancing of noncontrolling interest				(6,434)			(6,434)	$ 6,434
Other comprehensive income	12,811					12,302	12,302	509
Net income	48,989	0			47,400		47,400	1,589
Balance at Sep. 30, 2018	$ 1,560,797	$ 75,000	$ 1,078	$ 2,003,983	$ (589,785)	$ 16,485	$ 1,506,761	$ 54,036
Balance (in shares) at Sep. 30, 2018			107,825,791

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 8,876	$ 21,839	$ 48,989	$ 23,276
Adjustment to reconcile net income to net cash provided by operating activities:
Depreciation and amortization			125,221	110,286
Loss on impairments	0	0	2,934	0
Loss on involuntary conversion			0	330
Non-cash portion of interest expense			1,698	1,465
Intangible amortization in rental income, net	1,150	1,318	3,206	3,873
Straight-line rent adjustments, net			(8,297)	(4,855)
Dividends on forfeited equity compensation			15	2
Loss on extinguishment of debt	(13)	(13)	(13)	(15)
Gain on the sales of rental property, net			(32,276)	(19,225)
Non-cash compensation expense			6,671	7,159
Change in assets and liabilities:
Tenant accounts receivable, net			501	(955)
Prepaid expenses and other assets			(9,597)	(10,479)
Accounts payable, accrued expenses and other liabilities			9,249	5,572
Tenant prepaid rent and security deposits			283	3,570
Total adjustments			99,621	96,758
Net cash provided by operating activities			148,610	120,034
Cash flows from investing activities:
Acquisitions of land and buildings and improvements			(382,981)	(405,790)
Additions of land and building and improvements			(23,578)	(27,539)
Acquisitions of other assets			794	0
Acquisitions of other liabilities			(242)	0
Proceeds from sales of rental property, net			89,407	43,454
Proceeds from insurance on involuntary conversion			0	857
Acquisition deposits, net			(695)	685
Acquisitions of deferred leasing intangibles			(74,851)	(79,961)
Net cash used in investing activities			(393,250)	(468,294)
Cash flows from financing activities:
Proceeds from unsecured credit facility			643,000	538,000
Repayment of unsecured credit facility			(819,000)	(321,000)
Proceeds from unsecured term loans			150,000	0
Proceeds from unsecured notes			175,000	0
Repayment of mortgage notes			(1,379)	(105,027)
Payment of loan fees and costs			(4,451)	(1,185)
Dividends and distributions			117,146	103,655
Proceeds from sales of common stock			276,457	339,624
Redemption of preferred stock			70,000	0
Dividends and distributions			(1,524)	(969)
Offering costs			(3,191)	(4,746)
Net cash provided by financing activities			227,766	341,042
Decrease in cash and cash equivalents and restricted cash			(16,874)	(7,218)
Cash and cash equivalents and restricted cash—beginning of period			28,129	21,805	$ 21,805
Cash and cash equivalents and restricted cash—end of period	11,255	14,587	11,255	14,587	28,129
Supplemental disclosure:
Cash paid for interest, net of capitalized interest			31,875	30,476
Supplemental schedule of non-cash investing and financing activities
Issuance of units for acquisitions of land and building and improvements and deferred leasing intangibles			0	18,558
Acquisitions of land and buildings and improvements			232	17,304
Acquisitions of deferred leasing intangibles			48	2,064
Partial disposal of building due to involuntary conversion of building			0	363
Investing other receivables due to involuntary conversion of building			0	(363)
Change in additions of land, building, and improvements included in accounts payable, accrued expenses, and other liabilities			(1,475)	(13,201)
Additions to building and other capital improvements from non-cash compensation			(20)	(24)
Change in loan fees, costs, and offering costs included in accounts payable, accrued expenses, and other liabilities			48	30
Reclassification of preferred stock called for redemption to liability			70,000	0
Dividends and distributions payable	$ 14,530	$ 11,516	$ 14,530	$ 11,516	$ 11,880

Organization and Description of

Organization and Description of Business	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Description of Business	Organization and Description of Business STAG Industrial, Inc. (the “Company”) is an industrial real estate operating company focused on the acquisition and operation of single-tenant, industrial properties throughout the United States. The Company was formed as a Maryland corporation and has elected to be treated and intends to continue to qualify as a real estate investment trust (“REIT”) under Sections 856 through 860 of the Internal Revenue Code of 1986, as amended. The Company is structured as an umbrella partnership REIT, commonly called an UPREIT, and owns substantially all of its assets and conducts substantially all of its business through its operating partnership, STAG Industrial Operating Partnership, L.P., a Delaware limited partnership (the “Operating Partnership”). As of September 30, 2018 and December 31, 2017 , the Company owned a 96.4% and 95.9% , respectively, common equity interest in the Operating Partnership. The Company, through its wholly owned subsidiary, is the sole general partner of the Operating Partnership. As used herein, the “Company” refers to STAG Industrial, Inc. and its consolidated subsidiaries and partnerships, including the Operating Partnership, except where context otherwise requires. As of September 30, 2018 , the Company owned 381 buildings in 37 states with approximately 75.4 million rentable square feet, consisting of 313 warehouse/distribution buildings, 59 light manufacturing buildings, and 9 flex/office buildings. The Company’s buildings were approximately 95.4% leased to 330 tenants as of September 30, 2018 .

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Interim Financial Information The accompanying interim financial statements have been presented in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and with the instructions to Form 10-Q and Regulation S-X for interim financial information. Accordingly, these statements do not include all of the information and notes required by GAAP for complete financial statements. In the opinion of management, the accompanying interim financial statements include all adjustments, consisting of normal recurring items, necessary for their fair statement in conformity with GAAP. Interim results are not necessarily indicative of results for a full year. The year-end consolidated balance sheet data was derived from audited financial statements, but does not include all disclosures required by GAAP. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the Company’s consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2017 . Basis of Presentation The Company’s consolidated financial statements include the accounts of the Company, the Operating Partnership, and their subsidiaries. Interests in the Operating Partnership not owned by the Company are referred to as “Noncontrolling Common Units.” These Noncontrolling Common Units are held by other limited partners in the form of common units (“Other Common Units”) and long term incentive plan units (“LTIP units”) issued pursuant to the STAG Industrial, Inc. 2011 Equity Incentive Plan, as amended (the “2011 Plan”). All significant intercompany balances and transactions have been eliminated in the consolidation of entities. The financial statements of the Company are presented on a consolidated basis for all periods presented. Reclassifications and New Accounting Standards Certain prior year amounts have been reclassified to conform to the current year presentation. New Accounting Standards Adopted In August 2017, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities . The purpose of this updated guidance is to better align a company’s financial reporting for hedging activities with the economic objectives of those activities. This standard is effective for fiscal years beginning after December 15, 2018 and interim periods within those years, with early adoption permitted, and the Company adopted this standard effective January 1, 2018 using the modified retrospective transition method. The adoption of this standard resulted in a cumulative effect adjustment of approximately $0.3 million recorded as an increase to cumulative dividends in excess of earnings and an increase to accumulated other comprehensive income as of January 1, 2018 in the accompanying Consolidated Statements of Equity. In May 2017, the FASB issued ASU 2017-09, Stock Compensation (Topic 718): Scope of Modification Accounting , which provides updated guidance about which changes to the terms or conditions of a share-based payment award would require an entity to apply modification accounting under the topic. This standard is effective for fiscal years beginning after December 15, 2017 and interim periods within those years, and the Company adopted this standard prospectively effective January 1, 2018. The adoption of this standard did not have a material effect on the Company's consolidated financial statements. In February 2017, the FASB issued ASU 2017-05, Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20): Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets , which provides guidance for recognizing gains and losses from the transfer of nonfinancial assets in contracts with non-customers. The new standard was issued as part of the new revenue standard (ASU 2014-09, as discussed below), and defines “in substance nonfinancial asset,” unifies guidance related to partial sales of nonfinancial assets, eliminates rules specifically addressing sales of real estate, removes exceptions to the financial asset derecognition model, and clarifies the accounting for contributions of nonfinancial assets to joint ventures. As a result of the new guidance, the guidance specific to real estate sales in Subtopic 360-20 was eliminated, and sales and partial sales of real estate assets will now be subject to the same derecognition model as all other nonfinancial assets. This standard is effective at the same time an entity adopts ASU 2014-09, which the Company adopted effective January 1, 2018. The Company adopted this standard effective January 1, 2018 using the modified retrospective approach. The adoption of this standard did not have a material effect on the Company's consolidated financial statements. In January 2017, the FASB issued ASU 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business . The new standard provides a screen to determine when a set of assets and activities is not a business. The screen requires that when substantially all of the fair value of the gross assets acquired or disposed of is concentrated in a single identifiable asset or a group of similar identifiable assets, the set is not a business. This standard is effective for annual periods beginning after December 15, 2017 and interim periods within those periods, and the Company adopted this standard prospectively effective January 1, 2018. As a result, it is expected that the majority of the Company's acquisitions will be accounted for as asset acquisitions, whereas under the former guidance the majority of the Company's acquisitions had been accounted for as business combinations. The most significant difference between the two accounting models that impacts the Company's consolidated financial statements is that in an asset acquisition, property acquisition costs are generally a component of the consideration transferred to acquire a group of assets and are capitalized as a component of the cost of the assets, whereas in a business combination, property acquisition costs are expensed and not included as part of the consideration transferred. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash . The new standard requires that the statement of cash flows explain the changes during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. This standard is effective for fiscal years beginning after December 15, 2017 and the Company adopted this standard effective January 1, 2018. As a result, the Company has included restricted cash with cash and cash equivalents when reconciling the beginning and end of period total amounts on the accompanying Consolidated Statements of Cash Flows. The effects of this standard were applied retrospectively to all prior periods presented. For the nine months ended September 30, 2017 , the effect of the change in accounting principle was a decrease in cash provided by operating activities of approximately $0.5 million and an increase in cash used in investing activities of approximately $5.6 million on the accompanying Consolidated Statements of Cash Flows. In January 2016, the FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities (Subtopic 825-10) . The amendments in ASU 2016-01 address certain aspects of recognition, measurement, presentation, and disclosure of financial instruments. The standard primarily affects the accounting for equity investments, financial liabilities under the fair value option, and the presentation and disclosure requirements for financial instruments. ASU 2016-01 is effective for the annual periods beginning after December 31, 2017 and for annual periods and interim periods within those years, and the Company adopted this standard prospectively effective January 1, 2018. The adoption of this standard did not have a material effect on the Company's consolidated financial statements. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) . ASU 2014-09 is a comprehensive new revenue recognition model requiring a company to recognize revenue to depict the transfer of goods or services to a customer at an amount reflecting the consideration it expects to receive in exchange for those goods or services. Additionally, the new revenue guidance requires improved disclosures regarding the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. The Company adopted this standard effective January 1, 2018 using the modified retrospective approach. The adoption of this standard did not have a material effect on the Company's consolidated financial statements. New Accounting Standards Issued but not yet Adopted In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) , and various subsequent ASU’s, which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e. lessees and lessors). Topic 842 supersedes the previous leases standard, Topic 840, Leases . The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight line basis over the term of the lease, respectively. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less will be accounted for similar to existing guidance for operating leases today. The new standard requires lessors to account for leases using an approach that is substantially equivalent to existing guidance for sales-type leases, direct financing leases and operating leases. ASU 2016-02 is expected to impact the Company’s consolidated financial statements as the Company has certain operating and land lease arrangements for which it is the lessee, which will result in the recording of a right of use asset and the related lease liability. The standard is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, with early adoption permitted. The new standard must be adopted using the modified retrospective transition method by recognizing a cumulative effect adjustment to the opening balance of cumulative dividends in excess of earnings, by either applying the new guidance at the beginning of the earliest comparative period or by applying the new guidance at the adoption date. The Company intends to adopt available practical expedients which allows the Company to 1) not reassess whether any expired or existing contracts are or contain leases; 2) not reassess the lease classification for any expired or existing leases; and 3) not reassess initial direct costs for any existing leases. The Company is currently in the process of evaluating the impact the adoption of ASU 2016-02 will have on the Company’s financial position or results of operations, and plans to adopt this standard effective January 1, 2019. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , which the Company adopted on January 1, 2018, as discussed in “New Accounting Standards Adopted” above. While lease contracts with customers, which constitute a vast majority of the Company’s revenues, are specifically excluded from the model’s scope, once the new leases standard under ASU 2016-02 is adopted by the Company, the new revenue standard may apply to executory costs and other components of revenue due under leases that are deemed to be non-lease components (such as common area maintenance and provision of utilities), even when the revenue for such activities is not separately stipulated in the lease. In that case, revenue from these items previously recognized on a straight-line basis under current lease guidance would be recognized under the new revenue guidance as the related services are delivered. As a result, while the total revenue recognized over time would not differ under the new guidance, the recognition pattern may be different. In July 2018, the FASB issued ASU 2018-11 which amends Topic 842, Leases , and provides lessors with a practical expedient, by class of underlying asset, to not separate non-lease components from the associated lease component and, instead, to account for those components as a single component if the non-lease components otherwise would be accounted for under the new revenue guidance and both of the following are met: i) the timing and pattern of transfer of the non-lease component(s) and associated lease component are the same; and ii) the lease component, if accounted for separately, would be classified as an operating lease. Under this new expedient, if the non-lease components associated with the lease component are the predominant component of the combined component, a company should account for the combined component in accordance with Topic 606. Otherwise, the company should account for the combined component as an operating lease in accordance with Topic 842. The Company is currently in the process of evaluating the impact the adoption of ASU 2016-02 will have on the Company’s financial position or results of operations, and plans to adopt this standard effective January 1, 2019. Restricted Cash Restricted cash may include tenant security deposits and cash held in escrow for real estate taxes and capital improvements as required in various mortgage note agreements. Restricted cash also may include amounts held by the Company’s transfer agent for preferred stock dividends that are distributed subsequent to period end. The following table presents a reconciliation of cash and cash equivalents and restricted cash reported on the accompanying Consolidated Balance Sheets to amounts reported on the accompanying Consolidated Statements of Cash Flows. Reconciliation of cash and cash equivalents and restricted cash (in thousands) September 30, 2018 December 31, 2017 Cash and cash equivalents $ 6,024 $ 24,562 Restricted cash 5,231 3,567 Total cash and cash equivalents and restricted cash $ 11,255 $ 28,129 Tenant Accounts Receivable, net As of September 30, 2018 and December 31, 2017 , the Company had an allowance for doubtful accounts of approximately $0.6 million and $0.1 million , respectively. As of September 30, 2018 and December 31, 2017 , the Company had accrued rental income, net of allowance of approximately $30.7 million and $24.7 million , respectively. As of September 30, 2018 and December 31, 2017 , the Company had an allowance on accrued rental income of $0.2 million and $0.2 million , respectively. As of September 30, 2018 and December 31, 2017 , the Company had approximately $14.6 million and $12.7 million , respectively, of total lease security deposits available in the form of existing letters of credit, which are not reflected on the accompanying Consolidated Balance Sheets. As of September 30, 2018 and December 31, 2017 , the Company had approximately $0.7 million and $0.7 million , respectively, of lease security deposits available in cash, which are included in restricted cash on the accompanying Consolidated Balance Sheets. The Company's remaining lease security deposits are commingled in cash and cash equivalents. These funds may be used to settle tenant accounts receivables in the event of a default under the related lease. As of September 30, 2018 and December 31, 2017 , the Company's total liability associated with these lease security deposits was approximately $8.7 million and $8.1 million , respectively, and is included in tenant prepaid rent and security deposits on the accompanying Consolidated Balance Sheets. Revenue Recognition Tenant Recoveries The Company estimates that real estate taxes, which are the responsibility of certain tenants under the terms of their leases and are not reflected on the Company's consolidated financial statements, were approximately $3.8 million , $10.9 million , $2.9 million and $9.2 million for the three and nine months ended September 30, 2018 and 2017 , respectively. These amounts would have been the maximum real estate tax expense of the Company, excluding any penalties or interest, had the tenants not met their contractual obligations for these periods. Gain on the Sales of Rental Property, net The timing of the derecognition of a rental property and the corresponding recognition of gain on the sales of rental property, net is measured by various criteria related to the terms of the sale transaction, and if the Company has lost control of the property and the acquirer has gained control of the property after the transaction. If the derecognition criteria is met, the full gain is recognized. Taxes Federal Income Taxes The Company's taxable REIT subsidiaries recognized a net loss of approximately $22,000 , $0.1 million , $0.2 million and $0.4 million for the three and nine months ended September 30, 2018 and 2017 , respectively, which has been included on the accompanying Consolidated Statements of Operations. State and Local Income, Excise, and Franchise Tax State and local income, excise, and franchise taxes in the amount of $0.1 million , $0.6 million , $0.3 million and $0.7 million have been recorded in other expenses on the accompanying Consolidated Statements of Operations for the three and nine months ended September 30, 2018 and 2017 , respectively. Uncertain Tax Positions As of September 30, 2018 and December 31, 2017 , there were no liabilities for uncertain tax positions. Concentrations of Credit Risk Management believes the current credit risk portfolio is reasonably well diversified and does not contain any unusual concentration of credit risk.

Rental Property

Rental Property	9 Months Ended
	Sep. 30, 2018
Real Estate [Abstract]
Rental Property	Rental Property The following table summarizes the components of rental property as of September 30, 2018 and December 31, 2017 . Rental Property (in thousands) September 30, 2018 December 31, 2017 Land $ 355,590 $ 321,560 Buildings, net of accumulated depreciation of $190,538 and $160,281, respectivel y 2,006,013 1,756,579 Tenant improvements, net of accumulated depreciation of $35,495 and $32,714, respectively 30,577 30,138 Building and land improvements, net of accumulated depreciation of $75,754 and $56,062, respectivel y 160,496 143,170 Construction in progress 5,669 2,877 Deferred leasing intangibles, net of accumulated amortization of $237,892 and $280,642, respectively 327,734 313,253 Total rental property, net $ 2,886,079 $ 2,567,577 Acquisitions The following table summarizes the acquisitions of the Company during the three and nine months ended September 30, 2018 . Market (1) Date Acquired Square Feet Buildings Purchase Price Greenville/Spartanburg, SC January 11, 2018 203,000 1 $ 10,755 Minneapolis/St Paul, MN January 26, 2018 145,351 1 13,538 Philadelphia, PA February 1, 2018 278,582 1 18,277 Houston, TX February 22, 2018 242,225 2 22,478 Greenville/Spartanburg, SC March 30, 2018 222,710 1 13,773 Three months ended March 31, 2018 1,091,868 6 78,821 Chicago, IL April 23, 2018 169,311 2 10,975 Milwaukee/Madison, WI April 26, 2018 53,680 1 4,316 Pittsburgh, PA April 30, 2018 175,000 1 15,380 Detroit, MI May 9, 2018 274,500 1 19,328 Minneapolis/St Paul, MN May 15, 2018 509,910 2 26,983 Cincinnati/Dayton, OH May 23, 2018 158,500 1 7,317 Baton Rouge, LA May 31, 2018 279,236 1 21,379 Las Vegas, NV June 12, 2018 122,472 1 17,920 Greenville/Spartanburg, SC June 15, 2018 131,805 1 5,621 Denver, CO June 18, 2018 64,750 1 7,044 Cincinnati/Dayton, OH June 25, 2018 465,136 1 16,421 Charlotte, NC June 29, 2018 69,200 1 5,446 Houston, TX June 29, 2018 252,662 1 27,170 Three months ended June 30, 2018 2,726,162 15 185,300 Knoxville, TN July 10, 2018 106,000 1 6,477 Pittsburgh, PA August 2, 2018 265,568 1 19,186 Raleigh/Durham, NC August 2, 2018 365,000 1 21,067 Detroit, MI August 6, 2018 439,150 1 21,077 Des Moines, IA August 8, 2018 121,922 1 6,053 McAllen/Edinburg/Pharr, TX August 9, 2018 270,084 1 18,523 Pittsburgh, PA August 15, 2018 200,500 1 11,327 Minneapolis/St Paul, MN August 24, 2018 120,606 1 8,422 Milwaukee/Madison, WI September 28, 2018 100,800 1 7,484 Milwaukee/Madison, WI September 28, 2018 174,633 2 13,288 Chicago, IL September 28, 2018 105,637 1 6,368 Indianapolis, IN September 28, 2018 478,721 1 29,085 Augusta/Richmond County, GA September 28, 2018 203,726 1 9,379 Charlotte, NC September 28, 2018 301,000 1 16,807 Three months ended September 30, 2018 3,253,347 15 194,543 Nine months ended September 30, 2018 7,071,377 36 $ 458,664 (1) As defined by CoStar Realty Information Inc. The following table summarizes the allocation of the consideration paid at the date of acquisition during the nine months ended September 30, 2018 for the acquired assets and liabilities in connection with the acquisitions identified in the table above. Acquired Assets and Liabilities Purchase Price (in thousands) Weighted Average Amortization Period (years) of Intangibles at Acquisition Land $ 39,340 N/A Buildings 317,293 N/A Tenant improvements 4,849 N/A Building and land improvements 21,731 N/A Deferred leasing intangibles - In-place leases 52,276 8.7 Deferred leasing intangibles - Tenant relationships 21,861 11.8 Deferred leasing intangibles - Above market leases 4,062 8.2 Deferred leasing intangibles - Below market leases (3,122 ) 6.7 Deferred leasing intangibles - Above market ground leases (178 ) 48.1 Other assets 794 N/A Other liabilities (242 ) N/A Total purchase price $ 458,664 The table below sets forth the results of operations for the three and nine months ended September 30, 2018 for the buildings acquired during the nine months ended September 30, 2018 included in the Company’s Consolidated Statements of Operations from the date of acquisition. Results of Operations (in thousands) Three months ended September 30, 2018 Nine months ended September 30, 2018 Total revenue $ 7,122 $ 11,156 Net income $ 1,556 $ 1,642 Dispositions During the nine months ended September 30, 2018 , the Company sold 11 buildings comprised of approximately 2.0 million square feet with a net book value of approximately $57.1 million to third parties. These buildings contributed approximately $0.1 million , $2.7 million , $2.6 million and $7.7 million to revenue for the three and nine months ended September 30, 2018 and 2017 , respectively. These buildings contributed approximately $5,000 , $0.1 million , $0.5 million and $1.4 million to net income (exclusive of loss on involuntary conversion, loss on impairments, and gain on the sales of rental property, net) for the three and nine months ended September 30, 2018 and 2017 , respectively. Net proceeds from the sales of rental property were approximately $89.4 million and the Company recognized the full gain on the sales of rental property, net of approximately $32.3 million for the nine months ended September 30, 2018 . Loss on Impairments The following table summarizes the Company's loss on impairments for assets held and used during the nine months ended September 30, 2018 . Market (1) Buildings Event or Change in Circumstance Leading to Impairment Evaluation (2) Valuation technique utilized to estimate fair value Fair Value (3) Loss on Impairments (in thousands) Buena Vista, VA (4) 1 Change in estimated hold period (5) Discounted cash flows (6) Sergeant Bluff, IA (4) 1 Change in estimated hold period (5) Discounted cash flows (6) Three months ended March 31, 2018 $ 3,176 $ 2,934 Nine months ended September 30, 2018 $ 3,176 $ 2,934 (1) As defined by CoStar Realty Information Inc. (2) The Company tested the asset group for impairment utilizing a probability weighted recovery analysis of certain scenarios, and it was determined that the carrying value of the property and intangibles were not recoverable from the estimated future undiscounted cash flows. (3) The estimated fair value of the assets held and used is based on Level 3 inputs and is a non-recurring fair value measurement. Level 3 is defined as unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions. (4) These buildings do not have markets as defined by CoStar Realty Information Inc. (5) This property was sold during the nine months ended September 30, 2018 . (6) Level 3 inputs used to determine fair value for the impaired assets held and used for the three months ended March 31, 2018: discount rates ranged from 11.0% to 14.5% and exit capitalization rates ranged from 11.0% to 13.0% . Deferred Leasing Intangibles The following table sets forth the deferred leasing intangibles on the accompanying Consolidated Balance Sheets as of September 30, 2018 and December 31, 2017 . September 30, 2018 December 31, 2017 Deferred Leasing Intangibles (in thousands) Gross Accumulated Amortization Net Gross Accumulated Amortization Net Above market leases $ 70,454 $ (31,663 ) $ 38,791 $ 78,558 $ (36,810 ) $ 41,748 Other intangible lease assets 495,172 (206,229 ) 288,943 515,337 (243,832 ) 271,505 Total deferred leasing intangible assets $ 565,626 $ (237,892 ) $ 327,734 $ 593,895 $ (280,642 ) $ 313,253 Below market leases $ 33,751 $ (13,043 ) $ 20,708 $ 34,776 $ (13,555 ) $ 21,221 Total deferred leasing intangible liabilities $ 33,751 $ (13,043 ) $ 20,708 $ 34,776 $ (13,555 ) $ 21,221 The following table sets forth the amortization expense and the net decrease to rental income for the amortization of deferred leasing intangibles during the three and nine months ended September 30, 2018 and 2017 . Three months ended September 30, Nine months ended September 30, Deferred Leasing Intangibles Amortization (in thousands) 2018 2017 2018 2017 Net decrease to rental income related to above and below market lease amortization $ 1,150 $ 1,318 $ 3,206 $ 3,873 Amortization expense related to other intangible lease assets $ 20,361 $ 17,934 $ 56,698 $ 53,747 The following table sets forth the amortization of deferred leasing intangibles over the next five calendar years beginning with 2018 as of September 30, 2018 . Year Amortization Expense Related to Other Intangible Lease Assets (in thousands) Net Decrease to Rental Income Related to Above and Below Market Lease Amortization (in thousands) Remainder of 2018 $ 17,263 $ 927 2019 $ 57,841 $ 3,926 2020 $ 47,750 $ 3,546 2021 $ 37,229 $ 2,163 2022 $ 29,690 $ 1,154

Debt

Debt	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Debt	Debt The following table sets forth a summary of the Company’s outstanding indebtedness, including borrowings under the Company’s unsecured credit facility, unsecured term loans, unsecured notes, and mortgage notes as of September 30, 2018 and December 31, 2017 . Loan Principal Outstanding as of September 30, 2018 (in thousands) Principal Outstanding as of December 31, 2017 (in thousands) Interest (1) Maturity Date Prepayment Terms (2) Unsecured credit facility: Unsecured Credit Facility (3) $ 95,000 $ 271,000 L + 1.05% Jan-15-2023 i Total unsecured credit facility 95,000 271,000 Unsecured term loans: Unsecured Term Loan C 150,000 150,000 L + 1.30% Sep-29-2020 i Unsecured Term Loan B 150,000 150,000 L + 1.30% Mar-21-2021 i Unsecured Term Loan A 150,000 150,000 L + 1.30% Mar-31-2022 i Unsecured Term Loan D 150,000 — L + 1.30% Jan-04-2023 i Unsecured Term Loan E (4) — — L + 1.20% Jan-15-2024 i Total unsecured term loans 600,000 450,000 Less: Total unamortized deferred financing fees and debt issuance costs (3,915 ) (3,735 ) Total carrying value unsecured term loans, net 596,085 446,265 Unsecured notes: Series F Unsecured Notes 100,000 100,000 3.98 % Jan-05-2023 ii Series A Unsecured Notes 50,000 50,000 4.98 % Oct-1-2024 ii Series D Unsecured Notes 100,000 100,000 4.32 % Feb-20-2025 ii Series G Unsecured Notes 75,000 — 4.10 % Jun-13-2025 ii Series B Unsecured Notes 50,000 50,000 4.98 % Jul-1-2026 ii Series C Unsecured Notes 80,000 80,000 4.42 % Dec-30-2026 ii Series E Unsecured Notes 20,000 20,000 4.42 % Feb-20-2027 ii Series H Unsecured Notes 100,000 — 4.27 % Jun-13-2028 ii Total unsecured notes 575,000 400,000 Less: Total unamortized deferred financing fees and debt issuance costs (2,611 ) (1,766 ) Total carrying value unsecured notes, net 572,389 398,234 Mortgage notes (secured debt): Wells Fargo Bank, National Association CMBS Loan 53,652 54,949 4.31 % Dec-1-2022 iii Thrivent Financial for Lutherans 3,824 3,906 4.78 % Dec-15-2023 iv Total mortgage notes 57,476 58,855 Add: Total unamortized fair market value premiums 52 61 Less: Total unamortized deferred financing fees and debt issuance costs (535 ) (634 ) Total carrying value mortgage notes, net 56,993 58,282 Total / weighted average interest rate (5) $ 1,320,467 $ 1,173,781 3.69 % (1) Interest rate as of September 30, 2018 . At September 30, 2018 , the one-month LIBOR (“L”) was 2.26056% . The interest rate is not adjusted to include the amortization of deferred financing fees or debt issuance costs incurred in obtaining debt or any unamortized fair market value premiums. The spread over the applicable rate for the Company's unsecured credit facility and unsecured term loans is based on the Company's consolidated leverage ratio, as defined in the respective loan agreements. (2) Prepayment terms consist of (i) pre-payable with no penalty; (ii) pre-payable with penalty; (iii) pre-payable without penalty three months prior to the maturity date, however can be defeased beginning January 1, 2016; and (iv) pre-payable without penalty three months prior to the maturity date. (3) The capacity of the unsecured credit facility is $500.0 million . Deferred financing fees and debt issuance costs, net of accumulated amortization related to the unsecured credit facility of approximately $3.4 million and $1.5 million is included in prepaid expenses and other assets on the accompanying Consolidated Balance Sheets as of September 30, 2018 and December 31, 2017 , respectively. (4) Capacity of $175.0 million , which the Company has until July 25, 2019 to draw. (5) The weighted average interest rate was calculated using the fixed interest rate swapped on the notional amount of $600.0 million of debt that was in effect as of September 30, 2018 , and is not adjusted to include the amortization of deferred financing fees or debt issuance costs incurred in obtaining debt or any unamortized fair market value premiums. The aggregate undrawn nominal commitment on the unsecured credit facility and unsecured term loans as of September 30, 2018 was approximately $574.4 million , including issued letters of credit. The Company's actual borrowing capacity at any given point in time may be less and is restricted to a maximum amount based on the Company's debt covenant compliance. Total accrued interest for the Company's indebtedness was approximately $7.7 million and $5.6 million as of September 30, 2018 and December 31, 2017 , respectively, and is included in accounts payable, accrued expenses and other liabilities on the accompanying Consolidated Balance Sheets. The table below sets forth the costs included in interest expense related to the Company's debt arrangements on the accompanying Consolidated Statement of Operations for the three and nine months ended September 30, 2018 and 2017 . Three months ended September 30, Nine months ended September 30, Costs Included in Interest Expense (in thousands) 2018 2017 2018 2017 Amortization of deferred financing fees and debt issuance costs and fair market value premiums $ 617 $ 546 $ 1,698 $ 1,553 Facility fees and unused fees $ 275 $ 286 $ 928 $ 839 On July 26, 2018 , the Company closed on the refinancing of its unsecured credit facility. The refinancing transaction included extending the maturity date to January 15, 2023 , increasing the capacity to $500.0 million , and reducing the annual interest rate. As of September 30, 2018 , the interest rate on the unsecured credit facility was LIBOR plus a spread of 1.05% based on the Company’s consolidated leverage ratio, as defined in the credit agreement. The Company recognized a loss of approximately $13,000 as a result of the acceleration of unamortized deferred financing fees, which is included in loss on extinguishment of debt in the accompanying Consolidated Statements of Operations. The remaining unamortized deferred financing fees were carried over and will be amortized with any new deferred financing fees through the new maturity date of the unsecured credit facility. As of September 30, 2018 , the unsecured credit facility has an annual facility fee of 0.15% based on the Company’s consolidated leverage ratio, as defined in the credit agreement, of total commitments that is due and payable quarterly. The Company also is required to pay an annual fee of $50,000 . On July 26, 2018 , the Company entered into a $175.0 million unsecured term loan agreement ("Unsecured Term Loan E"). As of September 30, 2018 , the interest rate on the Unsecured Term Loan E was LIBOR plus a spread of 1.20% based on the Company's consolidated leverage ratio, as defined in the loan agreement. Unless otherwise terminated pursuant to the loan agreement, the Unsecured Term Loan E will mature on January 15, 2024 . The Unsecured Term Loan E has an accordion feature that allows the Company to increase its borrowing capacity to $350.0 million , subject to the satisfaction of certain conditions and lender consents. The agreement includes a delayed draw feature that allows the Company to draw up to six advances of at least $25.0 million each until July 25, 2019. To the extent that the Company does not request advances of the $175.0 million of aggregate commitments by July 25, 2019, the unadvanced commitments terminate. The Unsecured Term Loan E has an unused commitment fee equal to 0.15% of its unused commitments, which began to accrue on October 24, 2018 and is due and payable monthly until the earlier of (i) the date that commitments of $175.0 million have been fully advanced, (ii) July 26, 2019, and (iii) the date that commitments of $175.0 million have been reduced to zero pursuant to the terms of the agreement. The Company also is required to pay an annual fee of $35,000 . The Company and certain wholly owned subsidiaries of the Operating Partnership are guarantors of the Unsecured Term Loan E. The agreement also contains financial and other covenants substantially similar to the covenants in the Company's unsecured credit facility. On July 26, 2018, the Company entered into amendments to its unsecured term loan agreements to conform certain provisions to the Unsecured Term Loan E agreement and the new unsecured credit facility agreement. On April 10, 2018 , the Company entered into a note purchase agreement (“NPA”) for the private placement by the Operating Partnership of $75.0 million senior unsecured notes (“Series G Unsecured Notes”) maturing June 13, 2025 with a fixed annual interest rate of 4.10% , and $100.0 million senior unsecured notes (“Series H Unsecured Notes”) maturing June 13, 2028 with a fixed annual interest rate of 4.27% . The NPA contains a number of financial covenants substantially similar to the financial covenants contained in the Company’s unsecured credit facility and other unsecured notes. The Operating Partnership issued the Series G Unsecured Notes and the Series H Unsecured Notes on June 13, 2018. In addition, on April 10, 2018, the Company entered into amendments to the note purchase agreements related to the Company’s outstanding unsecured notes to conform certain provisions in the agreements to the provisions in the NPA. On March 28, 2018, the Company drew $75.0 million of the $150.0 million unsecured term loan that was entered into on July 28, 2017. On July 27, 2018, the Company drew the remaining $75.0 million of the $150.0 million unsecured term loan. Financial Covenant Considerations The Company was in compliance with all financial and other covenants as of September 30, 2018 and December 31, 2017 related to its unsecured credit facility, unsecured term loans, unsecured notes, and mortgage notes. The real estate net book value of the properties that are collateral for the Company’s debt arrangements was approximately $88.4 million and $90.9 million at September 30, 2018 and December 31, 2017 , respectively, and is limited to senior, property-level secured debt financing arrangements. Fair Value of Debt The following table presents the aggregate principal outstanding under the Company’s debt arrangements and the corresponding estimate of fair value as of September 30, 2018 and December 31, 2017 (in thousands). September 30, 2018 December 31, 2017 Principal Outstanding Fair Value Principal Outstanding Fair Value Unsecured credit facility $ 95,000 $ 95,000 $ 271,000 $ 271,528 Unsecured term loans 600,000 607,663 450,000 451,463 Unsecured notes 575,000 569,493 400,000 415,599 Mortgage notes 57,476 57,608 58,855 59,769 Total principal amount 1,327,476 $ 1,329,764 1,179,855 $ 1,198,359 Add: Total unamortized fair market value premiums 52 61 Less: Total unamortized deferred financing fees and debt issuance costs (7,061 ) (6,135 ) Total carrying value $ 1,320,467 $ 1,173,781 The applicable fair value guidance establishes a three tier value hierarchy, which prioritizes the inputs used in measuring fair value. These tiers include: Level 1, defined as observable inputs such as quoted prices in active markets; Level 2, defined as inputs other than quoted prices in active markets that are either directly or indirectly observable; and Level 3, defined as unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions. The fair value of the Company’s debt is based on Level 3 inputs.

Use of Derivative Financial Ins

Use of Derivative Financial Instruments	9 Months Ended
	Sep. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Use of Derivative Financial Instruments	Use of Derivative Financial Instruments Risk Management Objective of Using Derivatives The Company’s use of derivative instruments is limited to the utilization of interest rate swaps to manage interest rate risk exposure on existing and future liabilities and not for speculative purposes. The principal objective of such arrangements is to minimize the risks and related costs associated with the Company’s operating and financial structure. The following table details the Company’s outstanding interest rate swaps as of September 30, 2018 . All of the Company’s interest rate swaps are designated as qualifying cash flow hedges. Interest Rate Trade Date Effective Date Notional Amount Fair Value Pay Fixed Interest Rate Receive Variable Interest Rate Maturity Date Regions Bank Mar-01-2013 Mar-01-2013 $ 25,000 $ 471 1.3300 % One-month L Feb-14-2020 Capital One, N.A. Jun-13-2013 Jul-01-2013 $ 50,000 $ 703 1.6810 % One-month L Feb-14-2020 Capital One, N.A. Jun-13-2013 Aug-01-2013 $ 25,000 $ 344 1.7030 % One-month L Feb-14-2020 Regions Bank Sep-30-2013 Feb-03-2014 $ 25,000 $ 245 1.9925 % One-month L Feb-14-2020 The Toronto-Dominion Bank Oct-14-2015 Sep-29-2016 $ 25,000 $ 700 1.3830 % One-month L Sep-29-2020 PNC Bank, N.A. Oct-14-2015 Sep-29-2016 $ 50,000 $ 1,391 1.3906 % One-month L Sep-29-2020 Regions Bank Oct-14-2015 Sep-29-2016 $ 35,000 $ 978 1.3858 % One-month L Sep-29-2020 U.S. Bank, N.A. Oct-14-2015 Sep-29-2016 $ 25,000 $ 695 1.3950 % One-month L Sep-29-2020 Capital One, N.A. Oct-14-2015 Sep-29-2016 $ 15,000 $ 417 1.3950 % One-month L Sep-29-2020 Royal Bank of Canada Jan-08-2015 Mar-20-2015 $ 25,000 $ 684 1.7090 % One-month L Mar-21-2021 The Toronto-Dominion Bank Jan-08-2015 Mar-20-2015 $ 25,000 $ 682 1.7105 % One-month L Mar-21-2021 The Toronto-Dominion Bank Jan-08-2015 Sep-10-2017 $ 100,000 $ 1,488 2.2255 % One-month L Mar-21-2021 Wells Fargo, N.A. Jan-08-2015 Mar-20-2015 $ 25,000 $ 886 1.8280 % One-month L Mar-31-2022 The Toronto-Dominion Bank Jan-08-2015 Feb-14-2020 $ 25,000 $ 271 2.4535 % One-month L Mar-31-2022 Regions Bank Jan-08-2015 Feb-14-2020 $ 50,000 $ 520 2.4750 % One-month L Mar-31-2022 Capital One, N.A. Jan-08-2015 Feb-14-2020 $ 50,000 $ 467 2.5300 % One-month L Mar-31-2022 The Toronto-Dominion Bank Jul-20-2017 Oct-30-2017 $ 25,000 $ 1,054 1.8485 % One-month L Jan-04-2023 Royal Bank of Canada Jul-20-2017 Oct-30-2017 $ 25,000 $ 1,054 1.8505 % One-month L Jan-04-2023 Wells Fargo, N.A. Jul-20-2017 Oct-30-2017 $ 25,000 $ 1,055 1.8505 % One-month L Jan-04-2023 PNC Bank, N.A. Jul-20-2017 Oct-30-2017 $ 25,000 $ 1,052 1.8485 % One-month L Jan-04-2023 PNC Bank, N.A. Jul-20-2017 Oct-30-2017 $ 50,000 $ 2,105 1.8475 % One-month L Jan-04-2023 The Toronto-Dominion Bank Jul-24-2018 Jul-26-2019 $ 50,000 $ 111 2.9180 % One-month L Jan-12-2024 PNC Bank, N.A. Jul-24-2018 Jul-26-2019 $ 50,000 $ 106 2.9190 % One-month L Jan-12-2024 Bank of Montreal Jul-24-2018 Jul-26-2019 $ 50,000 $ 113 2.9190 % One-month L Jan-12-2024 U.S. Bank, N.A. Jul-24-2018 Jul-26-2019 $ 25,000 $ 57 2.9190 % One-month L Jan-12-2024 The fair value of the interest rate swaps outstanding as of September 30, 2018 and December 31, 2017 was as follows. Balance Sheet Line Item (in thousands) Notional Amount September 30, 2018 Fair Value Notional Amount December 31, 2017 Fair Value December 31, 2017 Interest rate swaps-Asset $ 900,000 $ 17,649 $ 475,000 $ 6,079 Interest rate swaps-Liability $ — $ — $ 250,000 $ (1,217 ) Cash Flow Hedges of Interest Rate Risk The Company’s objectives in using interest rate swaps are to add stability to interest expense and to manage its exposure to interest rate movements. For derivatives designated and that qualify as cash flow hedges of interest rate risk, the gain or loss on the derivative is recorded in accumulated other comprehensive income and subsequently reclassified into interest expense in the same periods during which the hedged transaction affects earnings. Amounts reported in accumulated other comprehensive income related to derivatives designated as qualifying cash flow hedges will be reclassified to interest expense as interest payments are made on the Company's variable rate debt. The Company estimates that approximately $5.1 million will be reclassified from accumulated other comprehensive income as a decrease to interest expense over the next 12 months. The table below presents the effect of cash flow hedge accounting and the location in the consolidated financial statements for the three and nine months ended September 30, 2018 and 2017 . Three months ended September 30, Nine months ended September 30, Effect of Cash Flow Hedge Accounting (in thousands) 2018 2017 2018 2017 Income (loss) recognized in accumulated other comprehensive income on interest rate swaps $ 2,572 $ 316 $ 13,349 $ (1,126 ) Income (loss) reclassified from accumulated other comprehensive income into income (loss) as interest expense $ 512 $ (282 ) $ 538 $ (1,426 ) Total interest expense presented in the Consolidated Statements of Operations in which the effects of cash flow hedges are recorded $ 12,698 $ 10,446 $ 35,602 $ 31,557 Credit-risk-related Contingent Features The Company has agreements with each of its derivative counterparties that contain a provision where the Company could be declared in default on its derivative obligations if repayment of the underlying indebtedness is accelerated by the lender due to the Company's default on the indebtedness. As of September 30, 2018 , the Company had no derivatives that were in a net liability position by counterparty. Fair Value of Interest Rate Swaps The Company’s valuation of the interest rate swaps is determined using widely accepted valuation techniques including discounted cash flow analysis on the expected cash flows of each derivative. This analysis reflects the contractual terms of the derivatives, including the period to maturity, and uses observable market-based inputs including interest rate curves. The Company incorporates credit valuation adjustments to appropriately reflect both its own nonperformance risk and the respective counterparty’s nonperformance risk in the fair value measurements. In adjusting the fair value of its derivative contracts for the effect of nonperformance risk, the Company has considered the impact of netting and any applicable credit enhancements, such as collateral postings, thresholds, mutual puts, and guarantees. Although the Company has determined that the majority of the inputs used to value its derivatives fall within Level 2 of the fair value hierarchy, the credit valuation adjustments associated with its derivatives utilize Level 3 inputs, such as estimates of current credit spreads to evaluate the likelihood of default by itself and its counterparties. However, as of September 30, 2018 and December 31, 2017 , the Company has assessed the significance of the impact of the credit valuation adjustments on the overall valuation of its derivative positions and has determined that the credit valuation adjustments are not significant to the overall valuation of its derivatives. As a result, the Company has determined that its derivative valuations in their entirety are classified in Level 2 of the fair value hierarchy. The following sets forth the Company’s financial instruments that are accounted for at fair value on a recurring basis as of September 30, 2018 and December 31, 2017 . Fair Value Measurements as of Balance Sheet Line Item (in thousands) Fair Value Level 1 Level 2 Level 3 Interest rate swaps-Asset $ 17,649 $ — $ 17,649 $ — Interest rate swaps-Liability $ — $ — $ — $ — Fair Value Measurements as of Balance Sheet Line Item (in thousands) Fair Value December 31, 2017 Level 1 Level 2 Level 3 Interest rate swaps-Asset $ 6,079 $ — $ 6,079 $ — Interest rate swaps-Liability $ (1,217 ) $ — $ (1,217 ) $ —

Equity

Equity	9 Months Ended
	Sep. 30, 2018
Stockholders' Equity Note [Abstract]
Equity	Equity Preferred Stock On June 11, 2018, the Company gave notice to redeem all 2,800,000 issued and outstanding shares of the 6.625% Series B Cumulative Redeemable Preferred Stock (“Series B Preferred Stock”). The Company recognized a deemed dividend to the holders of the Series B Preferred Stock of approximately $2.7 million on the accompanying Consolidated Statements of Operations for the nine months ended September 30, 2018 related to redemption costs and the original issuance costs of the Series B Preferred Stock. On July 11, 2018, the Company redeemed all of the Series B Preferred Stock. The table below sets forth the Company’s outstanding preferred stock issuances as of September 30, 2018 . Preferred Stock Issuances Issuance Date Number of Shares Liquidation Value Per Share Interest Rate 6.875% Series C Cumulative Redeemable Preferred Stock ( “ Series C Preferred Stock ” ) March 17, 2016 3,000,000 $ 25.00 6.875 % The tables below set forth the dividends attributable to the Company's outstanding preferred stock issuances during the nine months ended September 30, 2018 and the year ended December 31, 2017 . Quarter Ended 2018 Declaration Date Series B Series C Payment Date September 30 July 11, 2018 $ 0.0460069 (1) $ 0.4296875 October 1, 2018 June 30 April 10, 2018 0.4140625 0.4296875 July 2, 2018 March 31 February 14, 2018 0.4140625 0.4296875 April 2, 2018 Total $ 0.8741319 $ 1.2890625 (1) On June 11, 2018, the Company gave notice to redeem all 2,800,000 issued and outstanding shares of the Series B Preferred Stock. On July 11, 2018, the Company redeemed all of the Series B Preferred Stock at a cash redemption price of $25.00 per share, plus accrued and unpaid dividends to but excluding the redemption date, without interest. Quarter Ended 2017 Declaration Date Series B Preferred Stock Per Share Series C Preferred Stock Per Share Payment Date December 31 November 2, 2017 $ 0.4140625 $ 0.4296875 December 29, 2017 September 30 July 31, 2017 0.4140625 0.4296875 September 29, 2017 June 30 May 1, 2017 0.4140625 0.4296875 June 30, 2017 March 31 February 15, 2017 0.4140625 0.4296875 March 31, 2017 Total $ 1.6562500 $ 1.7187500 On October 10, 2018 , the Company’s board of directors declared the Series C Preferred Stock dividends for the quarter ending December 31, 2018 at a quarterly rate of $0.4296875 per share. Common Stock The following table sets forth the terms of the Company’s at-the market (“ATM”) common stock offering program as of September 30, 2018 . ATM Common Stock Offering Program Date Maximum Aggregate Offering Price (in thousands) Aggregate Common Stock Available as of 2017 $500 million ATM November 13, 2017 $ 500,000 $ 213,217 The table below set forth the activity under the ATM common stock offering programs during the nine months ended September 30, 2018 and year ended December 31, 2017 (in thousands, except share data). Nine months ended September 30, 2018 ATM Common Stock Offering Program Shares Weighted Average Price Per Share Gross Sales Net 2017 $500 million ATM 10,387,962 $ 26.61 $ 276,457 $ 2,888 $ 273,569 Total/weighted average 10,387,962 $ 26.61 $ 276,457 $ 2,888 $ 273,569 Year ended December 31, 2017 ATM Common Stock Offering Program Shares Weighted Average Price Per Share Gross Sales Net 2017 $500 million ATM 363,843 $ 28.38 $ 10,326 $ 129 $ 10,197 2017 $300 million ATM (1) 11,098,748 $ 27.03 300,000 3,637 296,363 2016 $228 million ATM (1) 4,799,784 $ 24.42 117,216 1,604 115,612 Total/weighted average 16,262,375 $ 26.29 $ 427,542 $ 5,370 $ 422,172 (1) These programs ended before December 31, 2017 . The table below sets forth the dividends attributable to the Company's outstanding shares of common stock that were declared during the nine months ended September 30, 2018 and the year ended December 31, 2017 . Month Ended 2018 Declaration Date Record Date Per Share Payment Date September 30 July 11, 2018 September 28, 2018 $ 0.118333 October 15, 2018 August 31 July 11, 2018 August 31, 2018 0.118333 September 17, 2018 July 31 July 11, 2018 July 31, 2018 0.118333 August 15, 2018 June 30 April 10, 2018 June 29, 2018 0.118333 July 16, 2018 May 31 April 10, 2018 May 31, 2018 0.118333 June 15, 2018 April 30 April 10, 2018 April 30, 2018 0.118333 May 15, 2018 March 31 November 2, 2017 March 29, 2018 0.118333 April 16, 2018 February 28 November 2, 2017 February 28, 2018 0.118333 March 15, 2018 January 31 November 2, 2017 January 31, 2018 0.118333 February 15, 2018 Total $ 1.064997 Month Ended 2017 Declaration Date Record Date Per Share Payment Date December 31 July 31, 2017 December 29, 2017 $ 0.117500 January 16, 2018 November 30 July 31, 2017 November 30, 2017 0.117500 December 15, 2017 October 31 July 31, 2017 October 31, 2017 0.117500 November 15, 2017 September 30 May 1, 2017 September 29, 2017 0.117500 October 16, 2017 August 31 May 1, 2017 August 31, 2017 0.117500 September 15, 2017 July 31 May 1, 2017 July 31, 2017 0.117500 August 15, 2017 June 30 February 15, 2017 June 30, 2017 0.116667 July 17, 2017 May 31 February 15, 2017 May 31, 2017 0.116667 June 15, 2017 April 30 February 15, 2017 April 28, 2017 0.116667 May 15, 2017 March 31 November 2, 2016 March 31, 2017 0.116667 April 17, 2017 February 28 November 2, 2016 February 28, 2017 0.116667 March 15, 2017 January 31 November 2, 2016 January 31, 2017 0.116667 February 15, 2017 Total $ 1.405002 On October 10, 2018 , the Company’s board of directors declared the common stock dividends for the months ending October 31, 2018 , November 30, 2018 and December 31, 2018 at a monthly rate of $0.118333 per share of common stock. Restricted Stock-Based Compensation Restricted shares of common stock granted on January 5, 2018 to certain employees of the Company, subject to the recipient’s continued employment, will vest in four equal installments on January 1 of each year beginning in 2019. The following table summarizes activity related to the Company’s unvested restricted shares of common stock for the nine months ended September 30, 2018 and the year ended December 31, 2017 . Unvested Restricted Shares of Common Stock Shares Balance at December 31, 2016 272,337 Granted 75,001 (1) Vested (109,209 ) (2) Forfeited (922 ) Balance at December 31, 2017 237,207 Granted 76,659 (1) Vested (112,405 ) (2) Forfeited (10,630 ) Balance at September 30, 2018 190,831 (1) The fair value per share on the grant date of January 5, 2018 and January 6, 2017 was $26.40 and $24.41 , respectively. (2) The Company repurchased and retired 41,975 and 40,836 restricted shares of common stock that vested during the nine months ended September 30, 2018 and the year ended December 31, 2017 , respectively. The unrecognized compensation expense associated with the Company’s restricted shares of common stock at September 30, 2018 was approximately $3.1 million and is expected to be recognized over a weighted average period of approximately 2.5 years . The following table summarizes the fair value at vesting for the restricted shares of common stock that vested during the three and nine months ended September 30, 2018 and 2017 . Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 Vested restricted shares of common stock — — 112,405 109,209 Fair value of vested restricted shares of common stock (in thousands) $ — $ — $ 3,002 $ 2,591

Noncontrolling Interest

Noncontrolling Interest	9 Months Ended
	Sep. 30, 2018
Noncontrolling Interest [Abstract]
Noncontrolling Interest	Noncontrolling Interest The table below summarizes the activity for noncontrolling interest in the Company for the nine months ended September 30, 2018 and the year ended December 31, 2017 . LTIP Units Other Common Units Total Noncontrolling Common Units Noncontrolling Interest Balance at December 31, 2016 1,576,516 2,057,365 3,633,881 4.3 % Granted/Issued 126,239 687,827 814,066 N/A Forfeited — — — N/A Conversions from LTIP units to Other Common Units (245,685 ) 245,685 — N/A Redemptions from Other Common Units to common stock — (351,260 ) (351,260 ) N/A Balance at December 31, 2017 1,457,070 2,639,617 4,096,687 4.1 % Granted/Issued 324,802 — 324,802 N/A Forfeited — — — N/A Conversions from LTIP units to Other Common Units (165,672 ) 165,672 — N/A Redemptions from Other Common Units to common stock — (352,055 ) (352,055 ) N/A Balance at September 30, 2018 1,616,200 2,453,234 4,069,434 3.6 % LTIP Units On March 12, 2018 , the Company's board of directors appointed Michelle Dilley to serve as director of the Company. On March 12, 2018 , Ms. Dilley was granted 3,930 LTIP units which, subject to Ms. Dilley's continued service, will vest on January 1, 2019. LTIP units granted on January 5, 2018 to non-employee, independent directors, subject to the recipient’s continued service, will vest on January 1, 2019. LTIP units granted on January 5, 2018 to certain senior executive officers and senior employees, subject to the recipient’s continued employment, will vest quarterly over four years, with the first vesting date having been March 31, 2018. Refer to Note 8 for a discussion of vested LTIP units granted on January 5, 2018 pursuant to the 2015 Outperformance Program (the “2015 OPP”). The fair value of the LTIP units at the date of grant was determined by a lattice-binomial option-pricing model based on a Monte Carlo simulation. The fair value of the LTIP units are based on Level 3 inputs and are non-recurring fair value measurements. The table below sets forth the assumptions used in valuing such LTIP units granted during the nine months ended September 30, 2018 (excluding those vested LTIP units granted pursuant to the 2015 OPP; refer to Note 8 for details). LTIP Units Assumptions Grant date March 12, 2018 January 5, 2018 Expected term (years) 10 10 Expected volatility 22.0 % 22.0 % Expected dividend yield 6.0 % 6.0 % Risk-free interest rate 2.46 % 2.09 % Fair value of LTIP units at issuance (in thousands) $ 90 $ 3,447 LTIP units at issuance 3,930 137,616 Fair value unit price per LTIP unit at issuance $ 22.90 $ 25.05 The following table summarizes activity related to the Company’s unvested LTIP units for the nine months ended September 30, 2018 and the year ended December 31, 2017 . Unvested LTIP Units LTIP Units Balance at December 31, 2016 403,423 Granted 126,239 Vested (229,355 ) Forfeited — Balance at December 31, 2017 300,307 Granted 324,802 Vested (342,940 ) Forfeited — Balance at September 30, 2018 282,169 The unrecognized compensation expense associated with the Company’s LTIP units at September 30, 2018 was approximately $5.7 million and is expected to be recognized over a weighted average period of approximately 2.5 years . The following table summarizes the fair value at vesting for the LTIP units that vested during the three and nine months ended September 30, 2018 and 2017 . Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 Vested LTIP units 30,949 44,942 342,940 157,816 Fair value of vested LTIP units (in thousands) $ 851 $ 1,235 $ 9,002 $ 4,146

Equity Incentive Plan

Equity Incentive Plan	9 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity Incentive Plan	Equity Incentive Plan At the Company’s annual meeting of stockholders held on April 30, 2018, the Company’s stockholders approved an amendment and restatement of the 2011 Plan, under which the Company may issue equity-based awards, including stock options, stock appreciation rights, restricted stock, restricted stock units, unrestricted stock awards and other awards based on shares of the Company’s common stock, such as LTIP units, to executive officers, directors, employees and other individuals providing bona fide services to or for the Company or its affiliates. The amendment increased the total number of shares of common stock authorized and reserved for issuance under the 2011 Plan by 3,000,000 shares to an aggregate of 6,642,461 shares, subject to certain adjustments as described in the 2011 Plan. Awards previously granted under the 2011 Plan will remain in effect pursuant to their terms. On January 5, 2018 , the Company granted performance units approved by the compensation committee of the board of directors, under the 2011 Plan to certain key employees of the Company. The terms of the performance units granted on January 5, 2018 are substantially the same as the terms of the performance units granted on January 6, 2017 and March 8, 2016, except that the measuring period commences on January 1, 2018 and ends on December 31, 2020. The fair value of the performance units at the date of grant was determined by a lattice-binomial option-pricing model based on a Monte Carlo simulation. The fair value of the performance units are based on Level 3 inputs and are non-recurring fair value measurements. The performance unit equity compensation expense is recognized into earnings ratably from the grant date over the respective vesting periods. The table below sets forth the assumptions used in valuing the performance units granted during the nine months ended September 30, 2018 . Performance Units Assumptions Grant date January 5, 2018 Expected volatility 22.0 % Expected dividend yield 6.0 % Risk-free interest rate 2.09 % Fair value of performance units grant (in thousands) $ 5,456 On January 1, 2018, the Company’s three year measurement period pursuant to the 2015 OPP concluded. It was determined that the Company's total stockholder return exceeded the threshold percentage and return hurdle and a pool of approximately $6.2 million was awarded to the participants. The compensation committee of the board of directors approved the issuance of 183,256 vested LTIP units and 53,722 vested shares of common stock (of which 15,183 shares of common stock were repurchased and retired) to the participants, all of which were issued on January 5, 2018 . The unrecognized compensation expense associated with the Company's performance units at September 30, 2018 was approximately $6.1 million and is expected to be recognized over a weighted average period of approximately 2.3 years . Non-cash Compensation Expense The following table summarizes the amount recorded in general and administrative expenses in the accompanying Consolidated Statements of Operations for the amortization of restricted shares of common stock, LTIP units, performance units, the 2015 OPP (performance units and the 2015 OPP, collectively the “Performance-based Compensation Plans”), and the Company’s director compensation for the three and nine months ended September 30, 2018 and 2017 . Three months ended September 30, Nine months ended September 30, Non-Cash Compensation Expense (in thousands) 2018 2017 2018 2017 Restricted shares of common stock $ 406 $ 594 $ 1,269 $ 1,776 LTIP units 893 1,167 2,654 3,508 Performance-based Compensation Plans 838 536 2,463 1,610 Director compensation (1) 99 87 285 265 Total non-cash compensation expense $ 2,236 $ 2,384 $ 6,671 $ 7,159 (1) All of the Company’s independent directors elected to receive shares of common stock in lieu of cash for their service during the three and nine months ended September 30, 2018 and 2017 . The number of shares of common stock granted is calculated based on the trailing 10 days average common stock price ending on the third business day preceding the grant date.

Earnings Per Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share During the three and nine months ended September 30, 2018 and 2017 , there were 193,117 , 196,871 , 237,207 and 238,129 , respectively, of unvested restricted shares of common stock on a weighted average basis that were considered participating securities. The following table sets forth the computation of basic and diluted earnings per common share for the three and nine months ended September 30, 2018 and 2017 . Three months ended September 30, Nine months ended September 30, Earnings Per Share (in thousands, except per share data) 2018 2017 2018 2017 Numerator Net income $ 8,876 $ 21,839 $ 48,989 $ 23,276 Less: preferred stock dividends 1,289 2,449 6,315 7,345 Less: redemption of preferred stock — — 2,661 — Less: amount allocated to participating securities 69 84 209 250 Less: income attributable to noncontrolling interest after preferred stock dividends 281 828 1,589 673 Net income attributable to common stockholders $ 7,237 $ 18,478 $ 38,215 $ 15,008 Denominator Weighted average common shares outstanding — basic 105,783 92,787 101,095 87,632 Effect of dilutive securities (1) Share-based compensation 550 648 400 606 Weighted average common shares outstanding — diluted 106,333 93,435 101,495 88,238 Net income per share — basic and diluted Net income per share attributable to common stockholders — basic $ 0.07 $ 0.20 $ 0.38 $ 0.17 Net income per share attributable to common stockholders — diluted $ 0.07 $ 0.20 $ 0.38 $ 0.17 (1) During the three and nine months ended September 30, 2018 and 2017 , there were approximately 193 , 197 , 237 and 238 , respectively, unvested restricted shares of common stock on a weighted average basis that were not included in the computation of diluted earnings per share because to do so would have been antidilutive for the period.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies The Company is subject to various legal proceedings and claims that arise in the ordinary course of business. These matters are generally covered by insurance subject to deductible requirements. Management believes that the ultimate settlement of these actions will not have a material adverse effect on the Company’s financial position, results of operations, or cash flows. The Company has letters of credit of approximately $5.6 million as of September 30, 2018 related to construction projects and certain other agreements.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events There were no recognized or non-recognized subsequent events.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Revenue Recognition, Real Estate Transactions, Policy [Policy Text Block]	Gain on the Sales of Rental Property, net The timing of the derecognition of a rental property and the corresponding recognition of gain on the sales of rental property, net is measured by various criteria related to the terms of the sale transaction, and if the Company has lost control of the property and the acquirer has gained control of the property after the transaction. If the derecognition criteria is met, the full gain is recognized.
Quarterly Financial Information	Interim Financial Information The accompanying interim financial statements have been presented in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and with the instructions to Form 10-Q and Regulation S-X for interim financial information. Accordingly, these statements do not include all of the information and notes required by GAAP for complete financial statements. In the opinion of management, the accompanying interim financial statements include all adjustments, consisting of normal recurring items, necessary for their fair statement in conformity with GAAP. Interim results are not necessarily indicative of results for a full year. The year-end consolidated balance sheet data was derived from audited financial statements, but does not include all disclosures required by GAAP. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the Company’s consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2017 .
Basis of Presentation	Basis of Presentation The Company’s consolidated financial statements include the accounts of the Company, the Operating Partnership, and their subsidiaries. Interests in the Operating Partnership not owned by the Company are referred to as “Noncontrolling Common Units.” These Noncontrolling Common Units are held by other limited partners in the form of common units (“Other Common Units”) and long term incentive plan units (“LTIP units”) issued pursuant to the STAG Industrial, Inc. 2011 Equity Incentive Plan, as amended (the “2011 Plan”). All significant intercompany balances and transactions have been eliminated in the consolidation of entities. The financial statements of the Company are presented on a consolidated basis for all periods presented.
Reclassification	Certain prior year amounts have been reclassified to conform to the current year presentation.
New Accounting Pronouncements	New Accounting Standards Adopted In August 2017, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities . The purpose of this updated guidance is to better align a company’s financial reporting for hedging activities with the economic objectives of those activities. This standard is effective for fiscal years beginning after December 15, 2018 and interim periods within those years, with early adoption permitted, and the Company adopted this standard effective January 1, 2018 using the modified retrospective transition method. The adoption of this standard resulted in a cumulative effect adjustment of approximately $0.3 million recorded as an increase to cumulative dividends in excess of earnings and an increase to accumulated other comprehensive income as of January 1, 2018 in the accompanying Consolidated Statements of Equity. In May 2017, the FASB issued ASU 2017-09, Stock Compensation (Topic 718): Scope of Modification Accounting , which provides updated guidance about which changes to the terms or conditions of a share-based payment award would require an entity to apply modification accounting under the topic. This standard is effective for fiscal years beginning after December 15, 2017 and interim periods within those years, and the Company adopted this standard prospectively effective January 1, 2018. The adoption of this standard did not have a material effect on the Company's consolidated financial statements. In February 2017, the FASB issued ASU 2017-05, Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20): Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets , which provides guidance for recognizing gains and losses from the transfer of nonfinancial assets in contracts with non-customers. The new standard was issued as part of the new revenue standard (ASU 2014-09, as discussed below), and defines “in substance nonfinancial asset,” unifies guidance related to partial sales of nonfinancial assets, eliminates rules specifically addressing sales of real estate, removes exceptions to the financial asset derecognition model, and clarifies the accounting for contributions of nonfinancial assets to joint ventures. As a result of the new guidance, the guidance specific to real estate sales in Subtopic 360-20 was eliminated, and sales and partial sales of real estate assets will now be subject to the same derecognition model as all other nonfinancial assets. This standard is effective at the same time an entity adopts ASU 2014-09, which the Company adopted effective January 1, 2018. The Company adopted this standard effective January 1, 2018 using the modified retrospective approach. The adoption of this standard did not have a material effect on the Company's consolidated financial statements. In January 2017, the FASB issued ASU 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business . The new standard provides a screen to determine when a set of assets and activities is not a business. The screen requires that when substantially all of the fair value of the gross assets acquired or disposed of is concentrated in a single identifiable asset or a group of similar identifiable assets, the set is not a business. This standard is effective for annual periods beginning after December 15, 2017 and interim periods within those periods, and the Company adopted this standard prospectively effective January 1, 2018. As a result, it is expected that the majority of the Company's acquisitions will be accounted for as asset acquisitions, whereas under the former guidance the majority of the Company's acquisitions had been accounted for as business combinations. The most significant difference between the two accounting models that impacts the Company's consolidated financial statements is that in an asset acquisition, property acquisition costs are generally a component of the consideration transferred to acquire a group of assets and are capitalized as a component of the cost of the assets, whereas in a business combination, property acquisition costs are expensed and not included as part of the consideration transferred. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash . The new standard requires that the statement of cash flows explain the changes during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. This standard is effective for fiscal years beginning after December 15, 2017 and the Company adopted this standard effective January 1, 2018. As a result, the Company has included restricted cash with cash and cash equivalents when reconciling the beginning and end of period total amounts on the accompanying Consolidated Statements of Cash Flows. The effects of this standard were applied retrospectively to all prior periods presented. For the nine months ended September 30, 2017 , the effect of the change in accounting principle was a decrease in cash provided by operating activities of approximately $0.5 million and an increase in cash used in investing activities of approximately $5.6 million on the accompanying Consolidated Statements of Cash Flows. In January 2016, the FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities (Subtopic 825-10) . The amendments in ASU 2016-01 address certain aspects of recognition, measurement, presentation, and disclosure of financial instruments. The standard primarily affects the accounting for equity investments, financial liabilities under the fair value option, and the presentation and disclosure requirements for financial instruments. ASU 2016-01 is effective for the annual periods beginning after December 31, 2017 and for annual periods and interim periods within those years, and the Company adopted this standard prospectively effective January 1, 2018. The adoption of this standard did not have a material effect on the Company's consolidated financial statements. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) . ASU 2014-09 is a comprehensive new revenue recognition model requiring a company to recognize revenue to depict the transfer of goods or services to a customer at an amount reflecting the consideration it expects to receive in exchange for those goods or services. Additionally, the new revenue guidance requires improved disclosures regarding the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. The Company adopted this standard effective January 1, 2018 using the modified retrospective approach. The adoption of this standard did not have a material effect on the Company's consolidated financial statements. New Accounting Standards Issued but not yet Adopted In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) , and various subsequent ASU’s, which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e. lessees and lessors). Topic 842 supersedes the previous leases standard, Topic 840, Leases . The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight line basis over the term of the lease, respectively. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less will be accounted for similar to existing guidance for operating leases today. The new standard requires lessors to account for leases using an approach that is substantially equivalent to existing guidance for sales-type leases, direct financing leases and operating leases. ASU 2016-02 is expected to impact the Company’s consolidated financial statements as the Company has certain operating and land lease arrangements for which it is the lessee, which will result in the recording of a right of use asset and the related lease liability. The standard is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, with early adoption permitted. The new standard must be adopted using the modified retrospective transition method by recognizing a cumulative effect adjustment to the opening balance of cumulative dividends in excess of earnings, by either applying the new guidance at the beginning of the earliest comparative period or by applying the new guidance at the adoption date. The Company intends to adopt available practical expedients which allows the Company to 1) not reassess whether any expired or existing contracts are or contain leases; 2) not reassess the lease classification for any expired or existing leases; and 3) not reassess initial direct costs for any existing leases. The Company is currently in the process of evaluating the impact the adoption of ASU 2016-02 will have on the Company’s financial position or results of operations, and plans to adopt this standard effective January 1, 2019. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , which the Company adopted on January 1, 2018, as discussed in “New Accounting Standards Adopted” above. While lease contracts with customers, which constitute a vast majority of the Company’s revenues, are specifically excluded from the model’s scope, once the new leases standard under ASU 2016-02 is adopted by the Company, the new revenue standard may apply to executory costs and other components of revenue due under leases that are deemed to be non-lease components (such as common area maintenance and provision of utilities), even when the revenue for such activities is not separately stipulated in the lease. In that case, revenue from these items previously recognized on a straight-line basis under current lease guidance would be recognized under the new revenue guidance as the related services are delivered. As a result, while the total revenue recognized over time would not differ under the new guidance, the recognition pattern may be different. In July 2018, the FASB issued ASU 2018-11 which amends Topic 842, Leases , and provides lessors with a practical expedient, by class of underlying asset, to not separate non-lease components from the associated lease component and, instead, to account for those components as a single component if the non-lease components otherwise would be accounted for under the new revenue guidance and both of the following are met: i) the timing and pattern of transfer of the non-lease component(s) and associated lease component are the same; and ii) the lease component, if accounted for separately, would be classified as an operating lease. Under this new expedient, if the non-lease components associated with the lease component are the predominant component of the combined component, a company should account for the combined component in accordance with Topic 606. Otherwise, the company should account for the combined component as an operating lease in accordance with Topic 842. The Company is currently in the process of evaluating the impact the adoption of ASU 2016-02 will have on the Company’s financial position or results of operations, and plans to adopt this standard effective January 1, 2019.
Restricted cash and cash equivalents, policy	Restricted Cash Restricted cash may include tenant security deposits and cash held in escrow for real estate taxes and capital improvements as required in various mortgage note agreements. Restricted cash also may include amounts held by the Company’s transfer agent for preferred stock dividends that are distributed subsequent to period end.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Cash, Cash Equivalents and Restricted Cash (Tables)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Schedule of Cash, Cash Equivalents and Restricted Cash	The following table presents a reconciliation of cash and cash equivalents and restricted cash reported on the accompanying Consolidated Balance Sheets to amounts reported on the accompanying Consolidated Statements of Cash Flows. Reconciliation of cash and cash equivalents and restricted cash (in thousands) September 30, 2018 December 31, 2017 Cash and cash equivalents $ 6,024 $ 24,562 Restricted cash 5,231 3,567 Total cash and cash equivalents and restricted cash $ 11,255 $ 28,129

Rental Property (Tables)

Rental Property (Tables)	9 Months Ended
	Sep. 30, 2018
Real Estate [Abstract]
Schedule of components of rental property	The following table summarizes the components of rental property as of September 30, 2018 and December 31, 2017 . Rental Property (in thousands) September 30, 2018 December 31, 2017 Land $ 355,590 $ 321,560 Buildings, net of accumulated depreciation of $190,538 and $160,281, respectivel y 2,006,013 1,756,579 Tenant improvements, net of accumulated depreciation of $35,495 and $32,714, respectively 30,577 30,138 Building and land improvements, net of accumulated depreciation of $75,754 and $56,062, respectivel y 160,496 143,170 Construction in progress 5,669 2,877 Deferred leasing intangibles, net of accumulated amortization of $237,892 and $280,642, respectively 327,734 313,253 Total rental property, net $ 2,886,079 $ 2,567,577
Schedule of real estate properties acquired	The following table summarizes the acquisitions of the Company during the three and nine months ended September 30, 2018 . Market (1) Date Acquired Square Feet Buildings Purchase Price Greenville/Spartanburg, SC January 11, 2018 203,000 1 $ 10,755 Minneapolis/St Paul, MN January 26, 2018 145,351 1 13,538 Philadelphia, PA February 1, 2018 278,582 1 18,277 Houston, TX February 22, 2018 242,225 2 22,478 Greenville/Spartanburg, SC March 30, 2018 222,710 1 13,773 Three months ended March 31, 2018 1,091,868 6 78,821 Chicago, IL April 23, 2018 169,311 2 10,975 Milwaukee/Madison, WI April 26, 2018 53,680 1 4,316 Pittsburgh, PA April 30, 2018 175,000 1 15,380 Detroit, MI May 9, 2018 274,500 1 19,328 Minneapolis/St Paul, MN May 15, 2018 509,910 2 26,983 Cincinnati/Dayton, OH May 23, 2018 158,500 1 7,317 Baton Rouge, LA May 31, 2018 279,236 1 21,379 Las Vegas, NV June 12, 2018 122,472 1 17,920 Greenville/Spartanburg, SC June 15, 2018 131,805 1 5,621 Denver, CO June 18, 2018 64,750 1 7,044 Cincinnati/Dayton, OH June 25, 2018 465,136 1 16,421 Charlotte, NC June 29, 2018 69,200 1 5,446 Houston, TX June 29, 2018 252,662 1 27,170 Three months ended June 30, 2018 2,726,162 15 185,300 Knoxville, TN July 10, 2018 106,000 1 6,477 Pittsburgh, PA August 2, 2018 265,568 1 19,186 Raleigh/Durham, NC August 2, 2018 365,000 1 21,067 Detroit, MI August 6, 2018 439,150 1 21,077 Des Moines, IA August 8, 2018 121,922 1 6,053 McAllen/Edinburg/Pharr, TX August 9, 2018 270,084 1 18,523 Pittsburgh, PA August 15, 2018 200,500 1 11,327 Minneapolis/St Paul, MN August 24, 2018 120,606 1 8,422 Milwaukee/Madison, WI September 28, 2018 100,800 1 7,484 Milwaukee/Madison, WI September 28, 2018 174,633 2 13,288 Chicago, IL September 28, 2018 105,637 1 6,368 Indianapolis, IN September 28, 2018 478,721 1 29,085 Augusta/Richmond County, GA September 28, 2018 203,726 1 9,379 Charlotte, NC September 28, 2018 301,000 1 16,807 Three months ended September 30, 2018 3,253,347 15 194,543 Nine months ended September 30, 2018 7,071,377 36 $ 458,664
Summary of allocation of the consideration paid for the acquired assets and liabilities in connection with the acquisition of buildings at the date of acquisition	The following table summarizes the allocation of the consideration paid at the date of acquisition during the nine months ended September 30, 2018 for the acquired assets and liabilities in connection with the acquisitions identified in the table above. Acquired Assets and Liabilities Purchase Price (in thousands) Weighted Average Amortization Period (years) of Intangibles at Acquisition Land $ 39,340 N/A Buildings 317,293 N/A Tenant improvements 4,849 N/A Building and land improvements 21,731 N/A Deferred leasing intangibles - In-place leases 52,276 8.7 Deferred leasing intangibles - Tenant relationships 21,861 11.8 Deferred leasing intangibles - Above market leases 4,062 8.2 Deferred leasing intangibles - Below market leases (3,122 ) 6.7 Deferred leasing intangibles - Above market ground leases (178 ) 48.1 Other assets 794 N/A Other liabilities (242 ) N/A Total purchase price $ 458,664
Schedule of pro forma information for acquired properties	The table below sets forth the results of operations for the three and nine months ended September 30, 2018 for the buildings acquired during the nine months ended September 30, 2018 included in the Company’s Consolidated Statements of Operations from the date of acquisition. Results of Operations (in thousands) Three months ended September 30, 2018 Nine months ended September 30, 2018 Total revenue $ 7,122 $ 11,156 Net income $ 1,556 $ 1,642
Impaired Assets to be Disposed of by Method Other than Sale [Table Text Block]	The following table summarizes the Company's loss on impairments for assets held and used during the nine months ended September 30, 2018 . Market (1) Buildings Event or Change in Circumstance Leading to Impairment Evaluation (2) Valuation technique utilized to estimate fair value Fair Value (3) Loss on Impairments (in thousands) Buena Vista, VA (4) 1 Change in estimated hold period (5) Discounted cash flows (6) Sergeant Bluff, IA (4) 1 Change in estimated hold period (5) Discounted cash flows (6) Three months ended March 31, 2018 $ 3,176 $ 2,934 Nine months ended September 30, 2018 $ 3,176 $ 2,934 (1) As defined by CoStar Realty Information Inc. (2) The Company tested the asset group for impairment utilizing a probability weighted recovery analysis of certain scenarios, and it was determined that the carrying value of the property and intangibles were not recoverable from the estimated future undiscounted cash flows. (3) The estimated fair value of the assets held and used is based on Level 3 inputs and is a non-recurring fair value measurement. Level 3 is defined as unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions. (4) These buildings do not have markets as defined by CoStar Realty Information Inc. (5) This property was sold during the nine months ended September 30, 2018 . (6) Level 3 inputs used to determine fair value for the impaired assets held and used for the three months ended March 31, 2018: discount rates ranged from 11.0% to 14.5% and exit capitalization rates ranged from 11.0% to 13.0% .
Schedule of Finite-Lived Intangible Assets and Below Market Leases	The following table sets forth the deferred leasing intangibles on the accompanying Consolidated Balance Sheets as of September 30, 2018 and December 31, 2017 . September 30, 2018 December 31, 2017 Deferred Leasing Intangibles (in thousands) Gross Accumulated Amortization Net Gross Accumulated Amortization Net Above market leases $ 70,454 $ (31,663 ) $ 38,791 $ 78,558 $ (36,810 ) $ 41,748 Other intangible lease assets 495,172 (206,229 ) 288,943 515,337 (243,832 ) 271,505 Total deferred leasing intangible assets $ 565,626 $ (237,892 ) $ 327,734 $ 593,895 $ (280,642 ) $ 313,253 Below market leases $ 33,751 $ (13,043 ) $ 20,708 $ 34,776 $ (13,555 ) $ 21,221 Total deferred leasing intangible liabilities $ 33,751 $ (13,043 ) $ 20,708 $ 34,776 $ (13,555 ) $ 21,221 The following table sets forth the amortization expense and the net decrease to rental income for the amortization of deferred leasing intangibles during the three and nine months ended September 30, 2018 and 2017 . Three months ended September 30, Nine months ended September 30, Deferred Leasing Intangibles Amortization (in thousands) 2018 2017 2018 2017 Net decrease to rental income related to above and below market lease amortization $ 1,150 $ 1,318 $ 3,206 $ 3,873 Amortization expense related to other intangible lease assets $ 20,361 $ 17,934 $ 56,698 $ 53,747
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	The following table sets forth the amortization of deferred leasing intangibles over the next five calendar years beginning with 2018 as of September 30, 2018 . Year Amortization Expense Related to Other Intangible Lease Assets (in thousands) Net Decrease to Rental Income Related to Above and Below Market Lease Amortization (in thousands) Remainder of 2018 $ 17,263 $ 927 2019 $ 57,841 $ 3,926 2020 $ 47,750 $ 3,546 2021 $ 37,229 $ 2,163 2022 $ 29,690 $ 1,154
Below Market Lease, Future Amortization Income	The following table sets forth the amortization of deferred leasing intangibles over the next five calendar years beginning with 2018 as of September 30, 2018 . Year Amortization Expense Related to Other Intangible Lease Assets (in thousands) Net Decrease to Rental Income Related to Above and Below Market Lease Amortization (in thousands) Remainder of 2018 $ 17,263 $ 927 2019 $ 57,841 $ 3,926 2020 $ 47,750 $ 3,546 2021 $ 37,229 $ 2,163 2022 $ 29,690 $ 1,154

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Summary of the mortgage notes payable, unsecured term loans and credit facility	The following table sets forth a summary of the Company’s outstanding indebtedness, including borrowings under the Company’s unsecured credit facility, unsecured term loans, unsecured notes, and mortgage notes as of September 30, 2018 and December 31, 2017 . Loan Principal Outstanding as of September 30, 2018 (in thousands) Principal Outstanding as of December 31, 2017 (in thousands) Interest (1) Maturity Date Prepayment Terms (2) Unsecured credit facility: Unsecured Credit Facility (3) $ 95,000 $ 271,000 L + 1.05% Jan-15-2023 i Total unsecured credit facility 95,000 271,000 Unsecured term loans: Unsecured Term Loan C 150,000 150,000 L + 1.30% Sep-29-2020 i Unsecured Term Loan B 150,000 150,000 L + 1.30% Mar-21-2021 i Unsecured Term Loan A 150,000 150,000 L + 1.30% Mar-31-2022 i Unsecured Term Loan D 150,000 — L + 1.30% Jan-04-2023 i Unsecured Term Loan E (4) — — L + 1.20% Jan-15-2024 i Total unsecured term loans 600,000 450,000 Less: Total unamortized deferred financing fees and debt issuance costs (3,915 ) (3,735 ) Total carrying value unsecured term loans, net 596,085 446,265 Unsecured notes: Series F Unsecured Notes 100,000 100,000 3.98 % Jan-05-2023 ii Series A Unsecured Notes 50,000 50,000 4.98 % Oct-1-2024 ii Series D Unsecured Notes 100,000 100,000 4.32 % Feb-20-2025 ii Series G Unsecured Notes 75,000 — 4.10 % Jun-13-2025 ii Series B Unsecured Notes 50,000 50,000 4.98 % Jul-1-2026 ii Series C Unsecured Notes 80,000 80,000 4.42 % Dec-30-2026 ii Series E Unsecured Notes 20,000 20,000 4.42 % Feb-20-2027 ii Series H Unsecured Notes 100,000 — 4.27 % Jun-13-2028 ii Total unsecured notes 575,000 400,000 Less: Total unamortized deferred financing fees and debt issuance costs (2,611 ) (1,766 ) Total carrying value unsecured notes, net 572,389 398,234 Mortgage notes (secured debt): Wells Fargo Bank, National Association CMBS Loan 53,652 54,949 4.31 % Dec-1-2022 iii Thrivent Financial for Lutherans 3,824 3,906 4.78 % Dec-15-2023 iv Total mortgage notes 57,476 58,855 Add: Total unamortized fair market value premiums 52 61 Less: Total unamortized deferred financing fees and debt issuance costs (535 ) (634 ) Total carrying value mortgage notes, net 56,993 58,282 Total / weighted average interest rate (5) $ 1,320,467 $ 1,173,781 3.69 % (1) Interest rate as of September 30, 2018 . At September 30, 2018 , the one-month LIBOR (“L”) was 2.26056% . The interest rate is not adjusted to include the amortization of deferred financing fees or debt issuance costs incurred in obtaining debt or any unamortized fair market value premiums. The spread over the applicable rate for the Company's unsecured credit facility and unsecured term loans is based on the Company's consolidated leverage ratio, as defined in the respective loan agreements. (2) Prepayment terms consist of (i) pre-payable with no penalty; (ii) pre-payable with penalty; (iii) pre-payable without penalty three months prior to the maturity date, however can be defeased beginning January 1, 2016; and (iv) pre-payable without penalty three months prior to the maturity date. (3) The capacity of the unsecured credit facility is $500.0 million . Deferred financing fees and debt issuance costs, net of accumulated amortization related to the unsecured credit facility of approximately $3.4 million and $1.5 million is included in prepaid expenses and other assets on the accompanying Consolidated Balance Sheets as of September 30, 2018 and December 31, 2017 , respectively. (4) Capacity of $175.0 million , which the Company has until July 25, 2019 to draw. (5) The weighted average interest rate was calculated using the fixed interest rate swapped on the notional amount of $600.0 million of debt that was in effect as of September 30, 2018 , and is not adjusted to include the amortization of deferred financing fees or debt issuance costs incurred in obtaining debt or any unamortized fair market value premiums
Interest Income and Interest Expense Disclosure [Table Text Block]	The table below sets forth the costs included in interest expense related to the Company's debt arrangements on the accompanying Consolidated Statement of Operations for the three and nine months ended September 30, 2018 and 2017 . Three months ended September 30, Nine months ended September 30, Costs Included in Interest Expense (in thousands) 2018 2017 2018 2017 Amortization of deferred financing fees and debt issuance costs and fair market value premiums $ 617 $ 546 $ 1,698 $ 1,553 Facility fees and unused fees $ 275 $ 286 $ 928 $ 839
Schedule of aggregate carrying value of the debt and the corresponding estimate of fair value	The following table presents the aggregate principal outstanding under the Company’s debt arrangements and the corresponding estimate of fair value as of September 30, 2018 and December 31, 2017 (in thousands). September 30, 2018 December 31, 2017 Principal Outstanding Fair Value Principal Outstanding Fair Value Unsecured credit facility $ 95,000 $ 95,000 $ 271,000 $ 271,528 Unsecured term loans 600,000 607,663 450,000 451,463 Unsecured notes 575,000 569,493 400,000 415,599 Mortgage notes 57,476 57,608 58,855 59,769 Total principal amount 1,327,476 $ 1,329,764 1,179,855 $ 1,198,359 Add: Total unamortized fair market value premiums 52 61 Less: Total unamortized deferred financing fees and debt issuance costs (7,061 ) (6,135 ) Total carrying value $ 1,320,467 $ 1,173,781

Use of Derivative Financial I_2

Use of Derivative Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments [Table Text Block]	The following table details the Company’s outstanding interest rate swaps as of September 30, 2018 . All of the Company’s interest rate swaps are designated as qualifying cash flow hedges. Interest Rate Trade Date Effective Date Notional Amount Fair Value Pay Fixed Interest Rate Receive Variable Interest Rate Maturity Date Regions Bank Mar-01-2013 Mar-01-2013 $ 25,000 $ 471 1.3300 % One-month L Feb-14-2020 Capital One, N.A. Jun-13-2013 Jul-01-2013 $ 50,000 $ 703 1.6810 % One-month L Feb-14-2020 Capital One, N.A. Jun-13-2013 Aug-01-2013 $ 25,000 $ 344 1.7030 % One-month L Feb-14-2020 Regions Bank Sep-30-2013 Feb-03-2014 $ 25,000 $ 245 1.9925 % One-month L Feb-14-2020 The Toronto-Dominion Bank Oct-14-2015 Sep-29-2016 $ 25,000 $ 700 1.3830 % One-month L Sep-29-2020 PNC Bank, N.A. Oct-14-2015 Sep-29-2016 $ 50,000 $ 1,391 1.3906 % One-month L Sep-29-2020 Regions Bank Oct-14-2015 Sep-29-2016 $ 35,000 $ 978 1.3858 % One-month L Sep-29-2020 U.S. Bank, N.A. Oct-14-2015 Sep-29-2016 $ 25,000 $ 695 1.3950 % One-month L Sep-29-2020 Capital One, N.A. Oct-14-2015 Sep-29-2016 $ 15,000 $ 417 1.3950 % One-month L Sep-29-2020 Royal Bank of Canada Jan-08-2015 Mar-20-2015 $ 25,000 $ 684 1.7090 % One-month L Mar-21-2021 The Toronto-Dominion Bank Jan-08-2015 Mar-20-2015 $ 25,000 $ 682 1.7105 % One-month L Mar-21-2021 The Toronto-Dominion Bank Jan-08-2015 Sep-10-2017 $ 100,000 $ 1,488 2.2255 % One-month L Mar-21-2021 Wells Fargo, N.A. Jan-08-2015 Mar-20-2015 $ 25,000 $ 886 1.8280 % One-month L Mar-31-2022 The Toronto-Dominion Bank Jan-08-2015 Feb-14-2020 $ 25,000 $ 271 2.4535 % One-month L Mar-31-2022 Regions Bank Jan-08-2015 Feb-14-2020 $ 50,000 $ 520 2.4750 % One-month L Mar-31-2022 Capital One, N.A. Jan-08-2015 Feb-14-2020 $ 50,000 $ 467 2.5300 % One-month L Mar-31-2022 The Toronto-Dominion Bank Jul-20-2017 Oct-30-2017 $ 25,000 $ 1,054 1.8485 % One-month L Jan-04-2023 Royal Bank of Canada Jul-20-2017 Oct-30-2017 $ 25,000 $ 1,054 1.8505 % One-month L Jan-04-2023 Wells Fargo, N.A. Jul-20-2017 Oct-30-2017 $ 25,000 $ 1,055 1.8505 % One-month L Jan-04-2023 PNC Bank, N.A. Jul-20-2017 Oct-30-2017 $ 25,000 $ 1,052 1.8485 % One-month L Jan-04-2023 PNC Bank, N.A. Jul-20-2017 Oct-30-2017 $ 50,000 $ 2,105 1.8475 % One-month L Jan-04-2023 The Toronto-Dominion Bank Jul-24-2018 Jul-26-2019 $ 50,000 $ 111 2.9180 % One-month L Jan-12-2024 PNC Bank, N.A. Jul-24-2018 Jul-26-2019 $ 50,000 $ 106 2.9190 % One-month L Jan-12-2024 Bank of Montreal Jul-24-2018 Jul-26-2019 $ 50,000 $ 113 2.9190 % One-month L Jan-12-2024 U.S. Bank, N.A. Jul-24-2018 Jul-26-2019 $ 25,000 $ 57 2.9190 % One-month L Jan-12-2024
Schedule of interest rate swaps	The fair value of the interest rate swaps outstanding as of September 30, 2018 and December 31, 2017 was as follows. Balance Sheet Line Item (in thousands) Notional Amount September 30, 2018 Fair Value Notional Amount December 31, 2017 Fair Value December 31, 2017 Interest rate swaps-Asset $ 900,000 $ 17,649 $ 475,000 $ 6,079 Interest rate swaps-Liability $ — $ — $ 250,000 $ (1,217 )
Schedule of the location in the financial statements of the gain or loss recognized on interest rate swaps	The table below presents the effect of cash flow hedge accounting and the location in the consolidated financial statements for the three and nine months ended September 30, 2018 and 2017 . Three months ended September 30, Nine months ended September 30, Effect of Cash Flow Hedge Accounting (in thousands) 2018 2017 2018 2017 Income (loss) recognized in accumulated other comprehensive income on interest rate swaps $ 2,572 $ 316 $ 13,349 $ (1,126 ) Income (loss) reclassified from accumulated other comprehensive income into income (loss) as interest expense $ 512 $ (282 ) $ 538 $ (1,426 ) Total interest expense presented in the Consolidated Statements of Operations in which the effects of cash flow hedges are recorded $ 12,698 $ 10,446 $ 35,602 $ 31,557
Schedule of financial instruments accounted for at fair value on a recurring basis	The following sets forth the Company’s financial instruments that are accounted for at fair value on a recurring basis as of September 30, 2018 and December 31, 2017 . Fair Value Measurements as of Balance Sheet Line Item (in thousands) Fair Value Level 1 Level 2 Level 3 Interest rate swaps-Asset $ 17,649 $ — $ 17,649 $ — Interest rate swaps-Liability $ — $ — $ — $ — Fair Value Measurements as of Balance Sheet Line Item (in thousands) Fair Value December 31, 2017 Level 1 Level 2 Level 3 Interest rate swaps-Asset $ 6,079 $ — $ 6,079 $ — Interest rate swaps-Liability $ (1,217 ) $ — $ (1,217 ) $ —

Equity (Tables)

Equity (Tables)	9 Months Ended
	Sep. 30, 2018
Stockholders' Equity Note [Abstract]
Schedule of Stock by Class	he table below sets forth the Company’s outstanding preferred stock issuances as of September 30, 2018 . Preferred Stock Issuances Issuance Date Number of Shares Liquidation Value Per Share Interest Rate 6.875% Series C Cumulative Redeemable Preferred Stock ( “ Series C Preferred Stock ” ) March 17, 2016 3,000,000 $ 25.00 6.875 %
Schedule of dividends	The tables below set forth the dividends attributable to the Company's outstanding preferred stock issuances during the nine months ended September 30, 2018 and the year ended December 31, 2017 . Quarter Ended 2018 Declaration Date Series B Series C Payment Date September 30 July 11, 2018 $ 0.0460069 (1) $ 0.4296875 October 1, 2018 June 30 April 10, 2018 0.4140625 0.4296875 July 2, 2018 March 31 February 14, 2018 0.4140625 0.4296875 April 2, 2018 Total $ 0.8741319 $ 1.2890625 (1) On June 11, 2018, the Company gave notice to redeem all 2,800,000 issued and outstanding shares of the Series B Preferred Stock. On July 11, 2018, the Company redeemed all of the Series B Preferred Stock at a cash redemption price of $25.00 per share, plus accrued and unpaid dividends to but excluding the redemption date, without interest. Quarter Ended 2017 Declaration Date Series B Preferred Stock Per Share Series C Preferred Stock Per Share Payment Date December 31 November 2, 2017 $ 0.4140625 $ 0.4296875 December 29, 2017 September 30 July 31, 2017 0.4140625 0.4296875 September 29, 2017 June 30 May 1, 2017 0.4140625 0.4296875 June 30, 2017 March 31 February 15, 2017 0.4140625 0.4296875 March 31, 2017 Total $ 1.6562500 $ 1.7187500 On October 10, 2018 , the Company’s board of directors declared the Series C Preferred Stock dividends for the quarter ending December 31, 2018 at a quarterly rate of $0.4296875 per share. The table below sets forth the dividends attributable to the Company's outstanding shares of common stock that were declared during the nine months ended September 30, 2018 and the year ended December 31, 2017 . Month Ended 2018 Declaration Date Record Date Per Share Payment Date September 30 July 11, 2018 September 28, 2018 $ 0.118333 October 15, 2018 August 31 July 11, 2018 August 31, 2018 0.118333 September 17, 2018 July 31 July 11, 2018 July 31, 2018 0.118333 August 15, 2018 June 30 April 10, 2018 June 29, 2018 0.118333 July 16, 2018 May 31 April 10, 2018 May 31, 2018 0.118333 June 15, 2018 April 30 April 10, 2018 April 30, 2018 0.118333 May 15, 2018 March 31 November 2, 2017 March 29, 2018 0.118333 April 16, 2018 February 28 November 2, 2017 February 28, 2018 0.118333 March 15, 2018 January 31 November 2, 2017 January 31, 2018 0.118333 February 15, 2018 Total $ 1.064997 Month Ended 2017 Declaration Date Record Date Per Share Payment Date December 31 July 31, 2017 December 29, 2017 $ 0.117500 January 16, 2018 November 30 July 31, 2017 November 30, 2017 0.117500 December 15, 2017 October 31 July 31, 2017 October 31, 2017 0.117500 November 15, 2017 September 30 May 1, 2017 September 29, 2017 0.117500 October 16, 2017 August 31 May 1, 2017 August 31, 2017 0.117500 September 15, 2017 July 31 May 1, 2017 July 31, 2017 0.117500 August 15, 2017 June 30 February 15, 2017 June 30, 2017 0.116667 July 17, 2017 May 31 February 15, 2017 May 31, 2017 0.116667 June 15, 2017 April 30 February 15, 2017 April 28, 2017 0.116667 May 15, 2017 March 31 November 2, 2016 March 31, 2017 0.116667 April 17, 2017 February 28 November 2, 2016 February 28, 2017 0.116667 March 15, 2017 January 31 November 2, 2016 January 31, 2017 0.116667 February 15, 2017 Total $ 1.405002 On October 10, 2018 , the Company’s board of directors declared the common stock dividends for the months ending October 31, 2018 , November 30, 2018 and December 31, 2018 at a monthly rate of $0.118333 per share of common stock.
Schedule of stock sale activity	The following table sets forth the terms of the Company’s at-the market (“ATM”) common stock offering program as of September 30, 2018 . ATM Common Stock Offering Program Date Maximum Aggregate Offering Price (in thousands) Aggregate Common Stock Available as of 2017 $500 million ATM November 13, 2017 $ 500,000 $ 213,217 The table below set forth the activity under the ATM common stock offering programs during the nine months ended September 30, 2018 and year ended December 31, 2017 (in thousands, except share data). Nine months ended September 30, 2018 ATM Common Stock Offering Program Shares Weighted Average Price Per Share Gross Sales Net 2017 $500 million ATM 10,387,962 $ 26.61 $ 276,457 $ 2,888 $ 273,569 Total/weighted average 10,387,962 $ 26.61 $ 276,457 $ 2,888 $ 273,569 Year ended December 31, 2017 ATM Common Stock Offering Program Shares Weighted Average Price Per Share Gross Sales Net 2017 $500 million ATM 363,843 $ 28.38 $ 10,326 $ 129 $ 10,197 2017 $300 million ATM (1) 11,098,748 $ 27.03 300,000 3,637 296,363 2016 $228 million ATM (1) 4,799,784 $ 24.42 117,216 1,604 115,612 Total/weighted average 16,262,375 $ 26.29 $ 427,542 $ 5,370 $ 422,172 (1) These programs ended before December 31, 2017 .
Schedule of activity related to unvested restricted stock awards	The following table summarizes activity related to the Company’s unvested restricted shares of common stock for the nine months ended September 30, 2018 and the year ended December 31, 2017 . Unvested Restricted Shares of Common Stock Shares Balance at December 31, 2016 272,337 Granted 75,001 (1) Vested (109,209 ) (2) Forfeited (922 ) Balance at December 31, 2017 237,207 Granted 76,659 (1) Vested (112,405 ) (2) Forfeited (10,630 ) Balance at September 30, 2018 190,831 (1) The fair value per share on the grant date of January 5, 2018 and January 6, 2017 was $26.40 and $24.41 , respectively. (2) The Company repurchased and retired 41,975 and 40,836 restricted shares of common stock that vested during the nine months ended September 30, 2018 and the year ended December 31, 2017 , respectively.
Schedule of vested restricted shares of common stock activity	The following table summarizes the fair value at vesting for the restricted shares of common stock that vested during the three and nine months ended September 30, 2018 and 2017 . Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 Vested restricted shares of common stock — — 112,405 109,209 Fair value of vested restricted shares of common stock (in thousands) $ — $ — $ 3,002 $ 2,591

Noncontrolling Interest (Tables

Noncontrolling Interest (Tables)	9 Months Ended
	Sep. 30, 2018
Noncontrolling Interest [Abstract]
Noncontrolling interest activity	The table below summarizes the activity for noncontrolling interest in the Company for the nine months ended September 30, 2018 and the year ended December 31, 2017 . LTIP Units Other Common Units Total Noncontrolling Common Units Noncontrolling Interest Balance at December 31, 2016 1,576,516 2,057,365 3,633,881 4.3 % Granted/Issued 126,239 687,827 814,066 N/A Forfeited — — — N/A Conversions from LTIP units to Other Common Units (245,685 ) 245,685 — N/A Redemptions from Other Common Units to common stock — (351,260 ) (351,260 ) N/A Balance at December 31, 2017 1,457,070 2,639,617 4,096,687 4.1 % Granted/Issued 324,802 — 324,802 N/A Forfeited — — — N/A Conversions from LTIP units to Other Common Units (165,672 ) 165,672 — N/A Redemptions from Other Common Units to common stock — (352,055 ) (352,055 ) N/A Balance at September 30, 2018 1,616,200 2,453,234 4,069,434 3.6 %
Schedule of share-based payment award, LTIP unit awards, valuation assumptions	The table below sets forth the assumptions used in valuing such LTIP units granted during the nine months ended September 30, 2018 (excluding those vested LTIP units granted pursuant to the 2015 OPP; refer to Note 8 for details). LTIP Units Assumptions Grant date March 12, 2018 January 5, 2018 Expected term (years) 10 10 Expected volatility 22.0 % 22.0 % Expected dividend yield 6.0 % 6.0 % Risk-free interest rate 2.46 % 2.09 % Fair value of LTIP units at issuance (in thousands) $ 90 $ 3,447 LTIP units at issuance 3,930 137,616 Fair value unit price per LTIP unit at issuance $ 22.90 $ 25.05
Schedule of activity related to unvested LTIP unit awards	The following table summarizes activity related to the Company’s unvested LTIP units for the nine months ended September 30, 2018 and the year ended December 31, 2017 . Unvested LTIP Units LTIP Units Balance at December 31, 2016 403,423 Granted 126,239 Vested (229,355 ) Forfeited — Balance at December 31, 2017 300,307 Granted 324,802 Vested (342,940 ) Forfeited — Balance at September 30, 2018 282,169
Schedule of vested LTIP unit award activity	The following table summarizes the fair value at vesting for the LTIP units that vested during the three and nine months ended September 30, 2018 and 2017 . Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 Vested LTIP units 30,949 44,942 342,940 157,816 Fair value of vested LTIP units (in thousands) $ 851 $ 1,235 $ 9,002 $ 4,146

Equity Incentive Plan (Tables)

Equity Incentive Plan (Tables)	9 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of share-based payment award, performance unit awards, valuation assumptions	The table below sets forth the assumptions used in valuing the performance units granted during the nine months ended September 30, 2018 . Performance Units Assumptions Grant date January 5, 2018 Expected volatility 22.0 % Expected dividend yield 6.0 % Risk-free interest rate 2.09 % Fair value of performance units grant (in thousands) $ 5,456
Summary of Equity Compensation Expense	The following table summarizes the amount recorded in general and administrative expenses in the accompanying Consolidated Statements of Operations for the amortization of restricted shares of common stock, LTIP units, performance units, the 2015 OPP (performance units and the 2015 OPP, collectively the “Performance-based Compensation Plans”), and the Company’s director compensation for the three and nine months ended September 30, 2018 and 2017 . Three months ended September 30, Nine months ended September 30, Non-Cash Compensation Expense (in thousands) 2018 2017 2018 2017 Restricted shares of common stock $ 406 $ 594 $ 1,269 $ 1,776 LTIP units 893 1,167 2,654 3,508 Performance-based Compensation Plans 838 536 2,463 1,610 Director compensation (1) 99 87 285 265 Total non-cash compensation expense $ 2,236 $ 2,384 $ 6,671 $ 7,159 (1) All of the Company’s independent directors elected to receive shares of common stock in lieu of cash for their service during the three and nine months ended September 30, 2018 and 2017 . The number of shares of common stock granted is calculated based on the trailing 10 days average common stock price ending on the third business day preceding the grant date.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Schedule of computation of basic and diluted earnings per common share	The following table sets forth the computation of basic and diluted earnings per common share for the three and nine months ended September 30, 2018 and 2017 . Three months ended September 30, Nine months ended September 30, Earnings Per Share (in thousands, except per share data) 2018 2017 2018 2017 Numerator Net income $ 8,876 $ 21,839 $ 48,989 $ 23,276 Less: preferred stock dividends 1,289 2,449 6,315 7,345 Less: redemption of preferred stock — — 2,661 — Less: amount allocated to participating securities 69 84 209 250 Less: income attributable to noncontrolling interest after preferred stock dividends 281 828 1,589 673 Net income attributable to common stockholders $ 7,237 $ 18,478 $ 38,215 $ 15,008 Denominator Weighted average common shares outstanding — basic 105,783 92,787 101,095 87,632 Effect of dilutive securities (1) Share-based compensation 550 648 400 606 Weighted average common shares outstanding — diluted 106,333 93,435 101,495 88,238 Net income per share — basic and diluted Net income per share attributable to common stockholders — basic $ 0.07 $ 0.20 $ 0.38 $ 0.17 Net income per share attributable to common stockholders — diluted $ 0.07 $ 0.20 $ 0.38 $ 0.17 (1) During the three and nine months ended September 30, 2018 and 2017 , there were approximately 193 , 197 , 237 and 238 , respectively, unvested restricted shares of common stock on a weighted average basis that were not included in the computation of diluted earnings per share because to do so would have been antidilutive for the period.

Organization and Description _2

Organization and Description of Business (Details) ft² in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018ft²tenantstatebuilding	Dec. 31, 2017
Real Estate Properties [Line Items]
Ownership interest in Operating Partnership (as a percent)	96.40%	95.90%
Number of properties	381
Number of states in which the entity owned buildings | state	37
Area (in square feet) | ft²	75.4
Percentage of buildings leased to tenants	95.40%
Number of tenants | tenant	330
Warehouse - Distribution buildings
Real Estate Properties [Line Items]
Number of properties	313
Light Manufacturing buildings
Real Estate Properties [Line Items]
Number of properties	59
Flex/Office Buildings
Real Estate Properties [Line Items]
Number of properties	9

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - New Accounting Pronouncements (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase to accumulated other comprehensive income (loss)	$ 16,485			$ 3,936
Increase in cash provided by operating activities	148,610	$ 120,034
Increase in cash used in investing activities	$ 393,250	468,294
Accounting Standards Update 2016-18 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in cash provided by operating activities		500
Increase in cash used in investing activities		$ (5,600)
New Accounting Pronouncement, Early Adoption, Effect [Member] | Accounting Standards Update 2017-12 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase to accumulated other comprehensive income (loss)			$ 300
Decrease in accumulated distributions in excess of net income			$ (300)

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 6,024	$ 24,562
Restricted cash	5,231	3,567
Cash and cash equivalents and restricted cash—end of period	$ 11,255	$ 28,129	$ 14,587	$ 21,805

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Tenant Accounts Receivable (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Tenant Accounts Receivable, net
Lease security deposits available in existing letters of credit	$ 14.6	$ 12.7
Lease security deposits in restricted cash	0.7	0.7
Lease security deposits included in tenant prepaid rent and security deposits on the Balance Sheet	8.7	8.1
Trade Accounts Receivable
Tenant Accounts Receivable, net
Allowance for doubtful accounts	0.6	0.1
Accrued Income Receivable
Tenant Accounts Receivable, net
Allowance for doubtful accounts	0.2	0.2
Deferred Rent Receivables, Net	$ 30.7	$ 24.7

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue Recognition
Estimated amount of real estate taxes, which are the responsibility of tenants	$ 3.8	$ 2.9	$ 10.9	$ 9.2

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Taxes (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Business Acquisition [Line Items]
Net income	$ 8,876,000	$ 21,839,000	$ 48,989,000	$ 23,276,000
State and local income, excise and franchise taxes	100,000	300,000	600,000	700,000
Liabilities for uncertain tax positions	0		0		$ 0
Real Estate Investment Trust
Business Acquisition [Line Items]
Net income	$ (22,000)	$ (200,000)	$ (100,000)	$ (400,000)

Rental Property - Summary (Deta

Rental Property - Summary (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Property Subject to or Available for Operating Lease [Line Items]
Rental property, net	$ 2,886,079	$ 2,567,577
Deferred leasing intangibles assets, accumulated amortization	237,892	280,642
Land
Property Subject to or Available for Operating Lease [Line Items]
Rental property, net	355,590	321,560
Buildings, net of accumulated depreciation of $190,538 and $160,281, respectively
Property Subject to or Available for Operating Lease [Line Items]
Rental property, net	2,006,013	1,756,579
Rental property, accumulated depreciation	190,538	160,281
Tenant improvements, net of accumulated depreciation of $35,495 and $32,714, respectively
Property Subject to or Available for Operating Lease [Line Items]
Rental property, net	30,577	30,138
Rental property, accumulated depreciation	35,495	32,714
Building and land improvements, net of accumulated depreciation of $75,754 and $56,062, respectively
Property Subject to or Available for Operating Lease [Line Items]
Rental property, net	160,496	143,170
Rental property, accumulated depreciation	75,754	56,062
Construction in progress
Property Subject to or Available for Operating Lease [Line Items]
Rental property, net	5,669	2,877
Deferred leasing intangibles, net of accumulated amortization of $280,642 and $280,642, respectively
Property Subject to or Available for Operating Lease [Line Items]
Rental property, net	327,734	313,253
Deferred leasing intangibles assets, accumulated amortization	$ 237,892	$ 280,642

Rental Property - Acquisitions

Rental Property - Acquisitions (Details) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018USD ($)ft²building	Jun. 30, 2018USD ($)ft²building	Mar. 31, 2018USD ($)ft²building	Sep. 30, 2018USD ($)ft²building
Business Acquisition [Line Items]
Area (in square feet)	75,400,000			75,400,000
Acquisitions 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)	7,071,377			7,071,377
Number of Buildings Acquired | building				36
Business Combination, Consideration Transferred | $				$ 458,664
Acquisitions Q1 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)			1,091,868
Number of Buildings Acquired | building			6
Business Combination, Consideration Transferred | $			$ 78,821
Fountain Inn, SC, Q1 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)			203,000
Number of Buildings Acquired | building			1
Business Combination, Consideration Transferred | $			$ 10,755
Bloomington, MN, Q1 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)			145,351
Number of Buildings Acquired | building			1
Business Combination, Consideration Transferred | $			$ 13,538
York, PA, Q1 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)			278,582
Number of Buildings Acquired | building			1
Business Combination, Consideration Transferred | $			$ 18,277
Houston, TX, Q1 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)			242,225
Number of Buildings Acquired | building			2
Business Combination, Consideration Transferred | $			$ 22,478
Greer, SC, Q1 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)			222,710
Number of Buildings Acquired | building			1
Business Combination, Consideration Transferred | $			$ 13,773
Acquisitions Q2 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)		2,726,162
Number of Buildings Acquired | building		15
Business Combination, Consideration Transferred | $		$ 185,300
McHenry, IL, Q2 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)		169,311
Number of Buildings Acquired | building		2
Business Combination, Consideration Transferred | $		$ 10,975
Caledonia, WI, Q2 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)		53,680
Number of Buildings Acquired | building		1
Business Combination, Consideration Transferred | $		$ 4,316
Clinton, PA, Q2 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)		175,000
Number of Buildings Acquired | building		1
Business Combination, Consideration Transferred | $		$ 15,380
Romulus, MI, Q2 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)		274,500
Number of Buildings Acquired | building		1
Business Combination, Consideration Transferred | $		$ 19,328
Mendota Heights, MN, Q2 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)		509,910
Number of Buildings Acquired | building		2
Business Combination, Consideration Transferred | $		$ 26,983
Fairfield, OH, Q2 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)		158,500
Number of Buildings Acquired | building		1
Business Combination, Consideration Transferred | $		$ 7,317
Baton Rouge, LA , Q2 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)		279,236
Number of Buildings Acquired | building		1
Business Combination, Consideration Transferred | $		$ 21,379
Las Vegas, NV , Q2 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)		122,472
Number of Buildings Acquired | building		1
Business Combination, Consideration Transferred | $		$ 17,920
Greer, SC , Q2 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)		131,805
Number of Buildings Acquired | building		1
Business Combination, Consideration Transferred | $		$ 5,621
Longmont, CO , Q2 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)		64,750
Number of Buildings Acquired | building		1
Business Combination, Consideration Transferred | $		$ 7,044
Florence, KY , Q2 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)		465,136
Number of Buildings Acquired | building		1
Business Combination, Consideration Transferred | $		$ 16,421
Charlotte, NC , Q2 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)		69,200
Number of Buildings Acquired | building		1
Business Combination, Consideration Transferred | $		$ 5,446
Conroe, TX , Q2 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)		252,662
Number of Buildings Acquired | building		1
Business Combination, Consideration Transferred | $		$ 27,170
Acquisitions Q3 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)	3,253,347			3,253,347
Number of Buildings Acquired | building	15
Business Combination, Consideration Transferred | $	$ 194,543
Knoxville, TN, Q3 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)	106,000			106,000
Number of Buildings Acquired | building	1
Business Combination, Consideration Transferred | $	$ 6,477
Pittsburgh, PA, Q3 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)	265,568			265,568
Number of Buildings Acquired | building	1
Business Combination, Consideration Transferred | $	$ 19,186
Raleigh/Durham, NC, Q3 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)	365,000			365,000
Number of Buildings Acquired | building	1
Business Combination, Consideration Transferred | $	$ 21,067
Detroit, MI, Q3 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)	439,150			439,150
Number of Buildings Acquired | building	1
Business Combination, Consideration Transferred | $	$ 21,077
Des Moines, IA, Q3 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)	121,922			121,922
Number of Buildings Acquired | building	1
Business Combination, Consideration Transferred | $	$ 6,053
McAllen/Edinburg/Pharr, TX, Q3 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)	270,084			270,084
Number of Buildings Acquired | building	1
Business Combination, Consideration Transferred | $	$ 18,523
Pittsburgh, PA2, Q3 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)	200,500			200,500
Number of Buildings Acquired | building	1
Business Combination, Consideration Transferred | $	$ 11,327
Minneapolis/St Paul, MN, Q3 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)	120,606			120,606
Number of Buildings Acquired | building	1
Business Combination, Consideration Transferred | $	$ 8,422
Milwaukee/Madison, WI, Q3 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)	100,800			100,800
Number of Buildings Acquired | building	1
Business Combination, Consideration Transferred | $	$ 7,484
Milwaukee/Madison, WI2, Q3 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)	174,633			174,633
Number of Buildings Acquired | building	2
Business Combination, Consideration Transferred | $	$ 13,288
Chicago, IL, Q3 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)	105,637			105,637
Number of Buildings Acquired | building	1
Business Combination, Consideration Transferred | $	$ 6,368
Indianapolis, IN, Q3 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)	478,721			478,721
Number of Buildings Acquired | building	1
Business Combination, Consideration Transferred | $	$ 29,085
Augusta/Richmond County, GA, Q3 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)	203,726			203,726
Number of Buildings Acquired | building	1
Business Combination, Consideration Transferred | $	$ 9,379
Charlotte, NC, Q3 2018 [Member]
Business Acquisition [Line Items]
Area (in square feet)	301,000			301,000
Number of Buildings Acquired | building	1
Business Combination, Consideration Transferred | $	$ 16,807

Rental Property - Acquisition_2

Rental Property - Acquisitions - Allocation of Consideration (Details) - Acquisitions 2018 [Member] $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)
Allocation of the consideration paid for the acquired assets and liabilities
Land	$ 39,340
Buildings	317,293
Tenant improvements	4,849
Building and land improvements	21,731
Other assets	794
Other liabilities	242
Total purchase price	458,664
In-place leases
Allocation of the consideration paid for the acquired assets and liabilities
Deferred leasing intangibles	$ (52,276)
Weighted average amortization period of lease intangibles	8 years 7 months 25 days
Tenant relationships
Allocation of the consideration paid for the acquired assets and liabilities
Deferred leasing intangibles	$ (21,861)
Weighted average amortization period of lease intangibles	11 years 9 months 10 days
Above market leases
Allocation of the consideration paid for the acquired assets and liabilities
Deferred leasing intangibles	$ (4,062)
Weighted average amortization period of lease intangibles	8 years 2 months 10 days
Below market leases
Allocation of the consideration paid for the acquired assets and liabilities
Deferred leasing intangibles	$ 3,122
Weighted average amortization period of lease intangibles	6 years 7 months 25 days
Above market ground leases
Allocation of the consideration paid for the acquired assets and liabilities
Deferred leasing intangibles	$ (178)
Weighted average amortization period of lease intangibles	48 years 1 month

Rental Property - Acquisition_3

Rental Property - Acquisitions - Results of Operations (Details) - Acquisitions 2018 [Member] - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Business Acquisition [Line Items]
Revenue	$ 7,122	$ 11,156
Net income (loss)	$ 1,556	$ 1,642

Rental Property - Disposals (De

Rental Property - Disposals (Details) ft² in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)ft²building	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)ft²building	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of buildings disposed | building	381		381
Area (in square feet) | ft²	75.4		75.4
Carrying value of property sold	$ 2,886,079,000		$ 2,886,079,000		$ 2,567,577,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 2018 Disposals [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of buildings disposed | building	11		11
Area (in square feet) | ft²	2		2
Carrying value of property sold	$ 57,100,000		$ 57,100,000
Contribution to revenue	100,000	$ 2,600,000	2,700,000	$ 7,700,000
Disposal Group, Including Discontinued Operation, Operating Income (Loss)	$ 5,000	$ 500,000	100,000	$ 1,400,000
Net proceeds from sales of rental property			89,400,000
Gain (Loss) on Sale			$ 32,300,000

Rental Property - Loss on Impai

Rental Property - Loss on Impairments (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Mar. 31, 2018USD ($)buildingRate	Sep. 30, 2018USD ($)
2018 Impairments [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on Impairment | $	$ 2,934	$ 2,934
2018 Impairments [Member] | Income Approach Valuation Technique | Fair Value, Inputs, Level 3
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Fair Value Disclosure | $	$ 3,176	$ 3,176
2018 Impairments [Member] | Income Approach Valuation Technique | Minimum | Fair Value, Inputs, Level 3
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Fair Value Inputs Exit Capitalization Rate	11.00%
2018 Impairments [Member] | Income Approach Valuation Technique | Maximum | Fair Value, Inputs, Level 3
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Fair Value Inputs Exit Capitalization Rate	13.00%
Buena Vista, VA, Q3 2012
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of Buildings Impaired | building	1
Sergeant Bluff, IA, Q4 2007
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of Buildings Impaired | building	1
Measurement Input, Discount Rate [Member] | 2018 Impairments [Member] | Income Approach Valuation Technique | Minimum | Fair Value, Inputs, Level 3
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Fair Value Inputs, Discount Rates	11.00%
Measurement Input, Discount Rate [Member] | 2018 Impairments [Member] | Income Approach Valuation Technique | Maximum | Fair Value, Inputs, Level 3
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Fair Value Inputs, Discount Rates	14.50%

Rental Property - Deferred Leas

Rental Property - Deferred Leasing Intangibles (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Deferred leasing intangibles, gross	$ 565,626		$ 565,626		$ 593,895
Deferred leasing intangibles assets, accumulated amortization	(237,892)		(237,892)		(280,642)
Deferred leasing intangibles, net	327,734		327,734		313,253
Below market lease, gross	33,751		33,751		34,776
Below market lease, accumulated amortization	(13,043)		(13,043)		(13,555)
Below market lease, net	20,708		20,708		21,221
Net decrease to rental revenue related to above and below market lease amortization	1,150	$ 1,318	3,206	$ 3,873
Above market leases
Finite-Lived Intangible Assets [Line Items]
Deferred leasing intangibles, gross	70,454		70,454		78,558
Deferred leasing intangibles assets, accumulated amortization	(31,663)		(31,663)		(36,810)
Deferred leasing intangibles, net	38,791		38,791		41,748
Net decrease to rental income related to above and below market lease amortization
Estimated Net Amortization of In-Place Leases, Leasing Commissions and Tenant Relationships
Remainder of 2018	927		927
2,019	3,926		3,926
2,020	3,546		3,546
2,021	2,163		2,163
2,022	1,154		1,154
Other intangible lease assets
Finite-Lived Intangible Assets [Line Items]
Deferred leasing intangibles, gross	495,172		495,172		515,337
Deferred leasing intangibles assets, accumulated amortization	(206,229)		(206,229)		(243,832)
Deferred leasing intangibles, net	288,943		288,943		$ 271,505
Amortization expense related to other intangible lease assets	20,361	$ 17,934	56,698	$ 53,747
Estimated Net Amortization of In-Place Leases, Leasing Commissions and Tenant Relationships
Remainder of 2018	17,263		17,263
2,019	57,841		57,841
2,020	47,750		47,750
2,021	37,229		37,229
2,022	$ 29,690		$ 29,690

Debt - Summary (Details)

Debt - Summary (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Jul. 26, 2018	Apr. 10, 2018
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,327,476	$ 1,179,855
Unamortized debt issuance costs	(7,061)	(6,135)
Debt Instrument, Unused Borrowing Capacity, Amount	574,400
Unamortized fair market value premium	52	61
Principal outstanding	$ 1,320,467	1,173,781
Weighted average interest rate	3.69%
Interest Rate Swaps
Debt Instrument [Line Items]
Notional amount	$ 600,000
London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Stated interest rate	2.26056%
$175 Million Unsecured Term Loan E [Member]
Debt Instrument [Line Items]
Debt Instrument, Unused Borrowing Capacity, Amount	$ 175,000
Mortgage Loans Payable
Debt Instrument [Line Items]
Long-term debt, gross	57,476	58,855
Unamortized debt issuance costs	(535)	(634)
Unamortized fair market value premium	52	61
Principal outstanding	56,993	58,282
Mortgage Loans Payable | Wells Fargo Bank, National Association CMBS Loan
Debt Instrument [Line Items]
Long-term debt, gross	$ 53,652	54,949
Stated interest rate	4.31%
Penalty free prepayment period	3 months
Mortgage Loans Payable | Thrivent Financial for Lutherans Due December 15, 2023 [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 3,824	3,906
Stated interest rate	4.78%
Penalty free prepayment period	3 months
Unsecured Term Loans
Debt Instrument [Line Items]
Long-term debt, gross	$ 600,000	450,000
Unamortized debt issuance costs	(3,915)	(3,735)
Principal outstanding	596,085	446,265
Unsecured Term Loans | $150 Million Wells Fargo Unsecured Term Loan C
Debt Instrument [Line Items]
Long-term debt, gross	$ 150,000	$ 150,000
Unsecured Term Loans | $150 Million Wells Fargo Unsecured Term Loan C | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest rate margin (as a percent)	1.30%	1.30%
Unsecured Term Loans | $150 Million Wells Fargo Unsecured Term Loan B
Debt Instrument [Line Items]
Long-term debt, gross	$ 150,000	$ 150,000
Unsecured Term Loans | $150 Million Wells Fargo Unsecured Term Loan B | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest rate margin (as a percent)	1.30%	1.30%
Unsecured Term Loans | $150 Million Wells Fargo Unsecured Term Loan A
Debt Instrument [Line Items]
Long-term debt, gross	$ 150,000	$ 150,000
Unsecured Term Loans | $150 Million Wells Fargo Unsecured Term Loan A | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest rate margin (as a percent)	1.30%	1.30%
Unsecured Term Loans | $150 Million Unsecured Term Loan D [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 150,000	$ 0
Unsecured Term Loans | $150 Million Unsecured Term Loan D [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest rate margin (as a percent)	1.30%	1.30%
Unsecured Term Loans | $175 Million Unsecured Term Loan E [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 0	$ 0	$ 175,000
Unsecured Term Loans | $175 Million Unsecured Term Loan E [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest rate margin (as a percent)	1.20%
Unsecured Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 575,000	400,000
Unamortized debt issuance costs	(2,611)	(1,766)
Principal outstanding	572,389	398,234
Unsecured Notes | $100 Million Series F Unsecured Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 100,000	100,000
Stated interest rate	3.98%
Unsecured Notes | $50 Million Series A Unsecured Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 50,000	50,000
Stated interest rate	4.98%
Unsecured Notes | $100 Million Series D Unsecured Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 100,000	100,000
Stated interest rate	4.32%
Unsecured Notes | $75 Million Series G Unsecured Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 75,000	0
Stated interest rate	4.10%			4.10%
Unsecured Notes | $50 Million Series B Unsecured Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 50,000	50,000
Stated interest rate	4.98%
Unsecured Notes | $80 Million Series C Unsecured Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 80,000	80,000
Stated interest rate	4.42%
Unsecured Notes | $20 Million Series E Unsecured Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 20,000	20,000
Stated interest rate	4.42%
Unsecured Notes | $100 Million Series H Unsecured Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 100,000	0
Stated interest rate	4.27%			4.27%
Unsecured Credit Facility
Debt Instrument [Line Items]
Principal outstanding	$ 95,000	$ 271,000
Maximum borrowing capacity	$ 500,000		$ 500,000
Unsecured Credit Facility | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest rate margin (as a percent)	1.05%	1.15%
Unsecured Credit Facility | Prepaid Expenses and Other Assets
Debt Instrument [Line Items]
Unamortized debt issuance costs	$ (3,400)	$ (1,500)

Debt - 2018 Activity (Details)

Debt - 2018 Activity (Details)	Jul. 27, 2018USD ($)	Mar. 28, 2018USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)advanceRate	Sep. 30, 2017USD ($)	Apr. 10, 2018USD ($)Rate	Dec. 31, 2017USD ($)
Debt Instrument [Line Items]
Debt Instrument, Unused Borrowing Capacity, Amount			$ 574,400,000		$ 574,400,000
Amortization of deferred financing fees			617,000	$ 546,000	1,698,000	$ 1,553,000
Net book value of properties that are collateral for debt arrangements			88,400,000		$ 88,400,000			$ 90,900,000
Unsecured Credit Facility
Debt Instrument [Line Items]
Write off of Deferred Debt Issuance Cost			13,000
Line of Credit Facility, Commitment Fee Percentage | Rate					0.15%
Debt Instrument, Fee Amount			50,000		$ 50,000
Accounts Payable and Accrued Liabilities [Member]
Debt Instrument [Line Items]
Interest payable			7,700,000		7,700,000			$ 5,600,000
$175 Million Unsecured Term Loan E [Member]
Debt Instrument [Line Items]
Debt Instrument, Unused Borrowing Capacity, Amount			175,000,000		175,000,000
$175 Million Unsecured Term Loan E [Member] | Unsecured Term Loans
Debt Instrument [Line Items]
Line of Credit Facility, Accordion Feature, Increase Limit			350,000,000		$ 350,000,000
Debt Instrument, Accordion Feature, Number of Advances, Maximum | advance					6
Debt Instrument, Accordion Feature, Increase Limit, Minimum Advance					$ 25,000,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage | Rate					0.15%
Debt Instrument, Fee Amount			$ 35,000		$ 35,000
$75 Million Series G Unsecured Notes [Member] | Unsecured Notes
Debt Instrument [Line Items]
Debt Instrument, Face Amount							$ 75,000,000
Stated interest rate			4.10%		4.10%		4.10%
$100 Million Series H Unsecured Notes [Member] | Unsecured Notes
Debt Instrument [Line Items]
Debt Instrument, Face Amount							$ 100,000,000
Stated interest rate			4.27%		4.27%		4.27%
$150 Million Unsecured Term Loan D [Member] | Unsecured Term Loans
Debt Instrument [Line Items]
Proceeds from Issuance of Debt	$ 75,000,000	$ 75,000,000
Interest Expense [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Commitment Fee Amount			$ 275,000	$ 286,000	$ 928,000	$ 839,000

Debt - Fair Value (Details)

Debt - Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,327,476	$ 1,179,855
Unamortized fair market value premium	52	61
Unamortized debt issuance costs	(7,061)	(6,135)
Principal outstanding	1,320,467	1,173,781
Long-term debt, fair value	1,329,764	1,198,359
Unsecured Credit Facility
Debt Instrument [Line Items]
Principal outstanding	95,000	271,000
Long-term debt, fair value	95,000	271,528
Unsecured Term Loans
Debt Instrument [Line Items]
Long-term debt, gross	600,000	450,000
Unamortized debt issuance costs	(3,915)	(3,735)
Principal outstanding	596,085	446,265
Long-term debt, fair value	607,663	451,463
Unsecured Notes
Debt Instrument [Line Items]
Long-term debt, gross	575,000	400,000
Unamortized debt issuance costs	(2,611)	(1,766)
Principal outstanding	572,389	398,234
Long-term debt, fair value	569,493	415,599
Mortgage Loans Payable
Debt Instrument [Line Items]
Long-term debt, gross	57,476	58,855
Unamortized fair market value premium	52	61
Unamortized debt issuance costs	(535)	(634)
Principal outstanding	56,993	58,282
Long-term debt, fair value	$ 57,608	$ 59,769

Use of Derivative Financial I_3

Use of Derivative Financial Instruments - Risk Management and Unsecured Loan Swaps (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Interest Rate Swaps
Unsecured Term Loan Swaps
Notional amount assets	$ 900,000	$ 475,000
Interest Rate Derivative, Regions Bank, March 01, 2013
Unsecured Term Loan Swaps
Notional amount assets	25,000
Fair value	$ 471
Fixed Interest Rate (as a percent)	1.33%
Interest Rate Derivative, Capital One, July 01, 2013
Unsecured Term Loan Swaps
Notional amount assets	$ 50,000
Fair value	$ 703
Fixed Interest Rate (as a percent)	1.681%
Interest Rate Derivative, Capital One, August 01, 2013
Unsecured Term Loan Swaps
Notional amount assets	$ 25,000
Fair value	$ 344
Fixed Interest Rate (as a percent)	1.703%
Interest Rate Derivative, Regions Bank, February 03, 2014
Unsecured Term Loan Swaps
Notional amount assets	$ 25,000
Fair value	$ 245
Fixed Interest Rate (as a percent)	1.9925%
Interest Rate Derivative, The Toronto-Dominion Bank, September 29, 2016
Unsecured Term Loan Swaps
Notional amount assets	$ 25,000
Fair value	$ 700
Fixed Interest Rate (as a percent)	1.383%
Interest Rate Derivative, PNC Bank, September 29, 2016
Unsecured Term Loan Swaps
Notional amount assets	$ 50,000
Fair value	$ 1,391
Fixed Interest Rate (as a percent)	1.3906%
Interest Rate Derivative, Regions Bank, September 29, 2016
Unsecured Term Loan Swaps
Notional amount assets	$ 35,000
Fair value	$ 978
Fixed Interest Rate (as a percent)	1.3858%
Interest Rate Derivative, US Bank, September 29, 2016
Unsecured Term Loan Swaps
Notional amount assets	$ 25,000
Fair value	$ 695
Fixed Interest Rate (as a percent)	1.395%
Interest Rate Derivative, Capital One, September 29, 2016
Unsecured Term Loan Swaps
Notional amount assets	$ 15,000
Fair value	$ 417
Fixed Interest Rate (as a percent)	1.395%
Interest Rate Derivative, Royal Bank of Canada, March 20, 2015
Unsecured Term Loan Swaps
Notional amount assets	$ 25,000
Fair value	$ 684
Fixed Interest Rate (as a percent)	1.709%
Interest Rate Derivative, The Toronto-Dominion Bank, March 20, 2015
Unsecured Term Loan Swaps
Notional amount assets	$ 25,000
Fair value	$ 682
Fixed Interest Rate (as a percent)	1.7105%
Interest Rate Derivative, The Toronto-Dominion Bank, September 10, 2017
Unsecured Term Loan Swaps
Notional amount assets	$ 100,000
Fair value	$ 1,488
Fixed Interest Rate (as a percent)	2.2255%
Interest Rate Derivative, Wells Fargo Bank, March 20, 2015
Unsecured Term Loan Swaps
Notional amount assets	$ 25,000
Fair value	$ 886
Fixed Interest Rate (as a percent)	1.828%
Interest Rate Derivative, The Toronto-Dominion Bank, February 14, 2020
Unsecured Term Loan Swaps
Notional amount assets	$ 25,000
Fair value	$ 271
Fixed Interest Rate (as a percent)	2.4535%
Interest Rate Derivative, Regions Bank, February 14, 2020
Unsecured Term Loan Swaps
Notional amount assets	$ 50,000
Fair value	$ 520
Fixed Interest Rate (as a percent)	2.475%
Interest Rate Derivative, Capital One, February 14, 2020
Unsecured Term Loan Swaps
Notional amount assets	$ 50,000
Fair value	$ 467
Fixed Interest Rate (as a percent)	2.53%
Interest Rate Derivative, The Toronto-Dominion Bank, October 30, 2017
Unsecured Term Loan Swaps
Notional amount assets	$ 25,000
Fair value	$ 1,054
Fixed Interest Rate (as a percent)	1.8485%
Interest Rate Derivative, Royal Bank of Canada, October 30, 2017
Unsecured Term Loan Swaps
Notional amount assets	$ 25,000
Fair value	$ 1,054
Fixed Interest Rate (as a percent)	1.8505%
Interest Rate Derivative, Wells Fargo Bank, October 30, 2017
Unsecured Term Loan Swaps
Notional amount assets	$ 25,000
Fair value	$ 1,055
Fixed Interest Rate (as a percent)	1.8505%
Interest Rate Derivative, PNC Bank, $25m, October 30, 2017
Unsecured Term Loan Swaps
Notional amount assets	$ 25,000
Fair value	$ 1,052
Fixed Interest Rate (as a percent)	1.8485%
Interest Rate Derivative, PNC Bank, $50m, October 30, 2017
Unsecured Term Loan Swaps
Notional amount assets	$ 50,000
Fair value	$ 2,105
Fixed Interest Rate (as a percent)	1.8475%
Interest Rate Derivative, The Toronto-Dominion Bank, July 26, 2019 [Member]
Unsecured Term Loan Swaps
Notional amount assets	$ 50,000
Fair value	$ 111
Fixed Interest Rate (as a percent)	2.918%
Interest Rate Derivative, PNC Bank, July 26, 2019 [Member]
Unsecured Term Loan Swaps
Notional amount assets	$ 50,000
Fair value	$ 106
Fixed Interest Rate (as a percent)	2.919%
Interest Rate Derivative, Bank of Montreal, July 26, 2019 [Member]
Unsecured Term Loan Swaps
Notional amount assets	$ 50,000
Fair value	$ 113
Fixed Interest Rate (as a percent)	2.919%
Interest Rate Derivative, US Bank, July 26, 2019 [Member]
Unsecured Term Loan Swaps
Notional amount assets	$ 25,000
Fair value	$ 57
Fixed Interest Rate (as a percent)	2.919%

Use of Derivative Financial I_4

Use of Derivative Financial Instruments - FV of Interest Rate Swaps (Details) - Interest Rate Swaps - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair value of the interest rate swaps outstanding
Notional amount assets	$ 900,000	$ 475,000
Fair value - assets	17,649	6,079
Notional amount liabilities	0	250,000
Fair Value - liabilities	$ 0	$ (1,217)

Use of Derivative Financial I_5

Use of Derivative Financial Instruments - Cash Flow Hedges and Contingent Features (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Cash Flow Hedges of Interest Rate Risk
Total interest expense presented in the Consolidated Statements of Operations in which the effects of cash flow hedges are recorded	$ 12,698	$ 10,446	$ 35,602	$ 31,557
Interest Rate Swaps
Cash Flow Hedges of Interest Rate Risk
Additional amount reclassified from accumulated other comprehensive income (loss) as a decrease to interest expense over the next twelve months	(5,100)		(5,100)
Income (loss) recognized in accumulated other comprehensive income on interest rate swaps	2,572	316	13,349	(1,126)
Income (loss) reclassified from accumulated other comprehensive income into income (loss) as interest expense	512	(282)	538	(1,426)
Total interest expense presented in the Consolidated Statements of Operations in which the effects of cash flow hedges are recorded	$ 12,698	$ 10,446	$ 35,602	$ 31,557

Use of Derivative Financial I_6

Use of Derivative Financial Instruments - FV on Recurring Basis (Details) - Interest Rate Swaps - Fair value on recurring basis - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets (liabilities):
Interest rate swaps-Asset	$ 17,649	$ 6,079
Interest rate swaps-Liability	0	(1,217)
Level 1
Assets (liabilities):
Interest rate swaps-Asset	0	0
Interest rate swaps-Liability	0	0
Level 2
Assets (liabilities):
Interest rate swaps-Asset	17,649	6,079
Interest rate swaps-Liability	0	(1,217)
Level 3
Assets (liabilities):
Interest rate swaps-Asset	0	0
Interest rate swaps-Liability	$ 0	$ 0

Equity - Preferred Stock (Detai

Equity - Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	Oct. 10, 2018	Jun. 11, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Jul. 11, 2018
Class of Stock [Line Items]
Preferred Stock Redemption Premium			$ 0				$ 0			$ 2,661	$ 0
Preferred stock, shares authorized			15,000,000			15,000,000				15,000,000		15,000,000
Preferred stock, par value (in dollars per share)			$ 0.01			$ 0.01				$ 0.01		$ 0.01
Series B Preferred Stock
Class of Stock [Line Items]
Stock Redeemed or Called During Period, Shares		2,800,000
Dividend rate (as a percent)		6.625%
Preferred Stock Redemption Premium										$ 2,700
Preferred Stock, Redemption Price Per Share													$ 25
Preferred stock, shares issued			0			2,800,000				0		2,800,000
Preferred stock, liquidation preference (in dollars per share)			$ 0			$ 25				$ 0		$ 25
Number of shares outstanding		2,800,000	0			2,800,000				0		2,800,000
Preferred Stock, Dividends Per Share, Declared			$ 0.0460069	$ 0.4140625	$ 0.4140625	$ 0.4140625	$ 0.4140625	$ 0.4140625	$ 0.4140625	$ 0.8741319		$ 1.6562500
Dividends Payable, Date Declared			Jul. 11, 2018	Apr. 10, 2018	Feb. 14, 2018	Nov. 2, 2017	Jul. 31, 2017	May 1, 2017	Feb. 15, 2017
Dividends Payable, Date to be Paid			Oct. 1, 2018	Jul. 2, 2018	Apr. 2, 2018	Dec. 29, 2017	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017
Series C Preferred Stock
Class of Stock [Line Items]
Dividend rate (as a percent)										6.875%
Preferred stock, shares issued			3,000,000			3,000,000				3,000,000		3,000,000
Preferred stock, liquidation preference (in dollars per share)			$ 25			$ 25				$ 25		$ 25
Number of shares outstanding			3,000,000			3,000,000				3,000,000		3,000,000
Preferred Stock, Dividends Per Share, Declared			$ 0.4296875	$ 0.4296875	$ 0.4296875	$ 0.4296875	$ 0.4296875	$ 0.4296875	$ 0.4296875	$ 1.2890625		$ 1.7187500
Dividends Payable, Date Declared			Jul. 11, 2018	Apr. 10, 2018	Feb. 14, 2018	Nov. 2, 2017	Jul. 31, 2017	May 1, 2017	Feb. 15, 2017
Dividends Payable, Date to be Paid			Oct. 1, 2018	Jul. 2, 2018	Apr. 2, 2018	Dec. 29, 2017	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017
Series C Preferred Stock | Scenario, Forecast [Member]
Class of Stock [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0.4296875

Equity - Common Stock ATM (Deta

Equity - Common Stock ATM (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Class of Stock [Line Items]
Proceeds from sales of common stock	$ 276,457	$ 339,624
At The Market Program 2017 $500 Million | Common Stock
Class of Stock [Line Items]
Common Stock Value Authorized under Stock Offering Program	500,000
Aggregate value of common stock available to be sold under the ATM	$ 213,217
Number of shares sold	10,387,962		363,843
Proceeds from sales of common stock	$ 276,457		$ 10,326
Sales agents' fee	2,888		129
Net proceeds	$ 273,569		$ 10,197
At The Market Program 2017 $300 Million | Common Stock
Class of Stock [Line Items]
Number of shares sold			11,098,748
Proceeds from sales of common stock			$ 300,000
Sales agents' fee			3,637
Net proceeds			$ 296,363
At The Market Program 2016 $228 Million | Common Stock
Class of Stock [Line Items]
Number of shares sold			4,799,784
Proceeds from sales of common stock			$ 117,216
Sales agents' fee			1,604
Net proceeds			$ 115,612
At The Market (ATM) Program | Common Stock
Class of Stock [Line Items]
Number of shares sold	10,387,962		16,262,375
Proceeds from sales of common stock	$ 276,457		$ 427,542
Sales agents' fee	2,888		5,370
Net proceeds	$ 273,569		$ 422,172
Weighted Average | At The Market Program 2017 $500 Million | Common Stock
Class of Stock [Line Items]
Issue price (in dollars per share)	$ 26.61		$ 28.38
Weighted Average | At The Market Program 2017 $300 Million | Common Stock
Class of Stock [Line Items]
Issue price (in dollars per share)			27.03
Weighted Average | At The Market Program 2016 $228 Million | Common Stock
Class of Stock [Line Items]
Issue price (in dollars per share)			24.42
Weighted Average | At The Market (ATM) Program | Common Stock
Class of Stock [Line Items]
Issue price (in dollars per share)	$ 26.61		$ 26.29

Equity - Common Stock Dividends

Equity - Common Stock Dividends (Details) - Common Stock - $ / shares	Oct. 15, 2018	Oct. 10, 2018	Sep. 17, 2018	Aug. 15, 2018	Jul. 16, 2018	Jul. 11, 2018	Jun. 15, 2018	May 15, 2018	Apr. 16, 2018	Apr. 10, 2018	Mar. 15, 2018	Feb. 15, 2018	Jan. 16, 2018	Dec. 15, 2017	Nov. 15, 2017	Nov. 02, 2017	Oct. 16, 2017	Sep. 15, 2017	Aug. 15, 2017	Jul. 31, 2017	Jul. 17, 2017	Jun. 15, 2017	May 15, 2017	May 01, 2017	Apr. 17, 2017	Mar. 15, 2017	Feb. 15, 2017	Nov. 02, 2016	Sep. 30, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Common Stock, Dividends, Per Share, Cash Paid			$ 0.118333	$ 0.118333	$ 0.118333		$ 0.118333	$ 0.118333	$ 0.118333		$ 0.118333	$ 0.118333	$ 0.117500	$ 0.117500	$ 0.117500		$ 0.117500	$ 0.117500	$ 0.117500		$ 0.116667	$ 0.116667	$ 0.116667		$ 0.116667	$ 0.116667	$ 0.116667		$ 1.064997	$ 1.405002
Common Stock, Dividends, Per Share, Declared						$ 0.118333				$ 0.118333						$ 0.118333				$ 0.117500				$ 0.117500			$ 0.116667	$ 0.116667	$ 1.064997	$ 1.405002
Scenario, Forecast [Member]
Class of Stock [Line Items]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.118333
Common Stock, Dividends, Per Share, Declared		$ 0.118333

Equity - Restricted Stock (Deta

Equity - Restricted Stock (Details) - Restricted stock - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Shares
Unvested at beginning of period (in shares)			237,207	272,337	272,337
Granted (in shares)			76,659		75,001
Vested (in shares)	0	0	(112,405)	(109,209)	(109,209)
Forfeited (in shares)			(10,630)		(922)
Unvested at end of period (in shares)	190,831		190,831		237,207
Stock Repurchased and Retired During Period, Shares			41,975		40,836
Unrecognized compensation costs	$ 3,100		$ 3,100
Unrecognized compensation costs, period for recognition			2 years 5 months 20 days
Vested (in shares)	0	0	(112,405)	(109,209)	(109,209)
Fair value of shares vested	$ 0	$ 0	$ 3,002	$ 2,591
Granted on January 5, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)			4 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value			$ 26.40
Granted on January 6, 2017 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value					$ 24.41

Noncontrolling Interest - Summa

Noncontrolling Interest - Summary (Details) - shares	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Noncontrolling interest
Noncontrolling interest ownership percentage	3.60%	4.10%	4.30%
Noncontrolling Interest - Unit holders in Operating Partnership
Noncontrolling interest
Units outstanding, balance at beginning of period (in units)	4,096,687	3,633,881
Granted/Issued	324,802	814,066
Forfeited	0	0
Conversions from LTIP units to Other Common Units	0	0
Redemptions from Other Common Units to common stock	352,055	351,260
Units outstanding, balance at end of period (in units)	4,069,434	4,096,687
LTIP Units | Noncontrolling Interest - Unit holders in Operating Partnership
Noncontrolling interest
Units outstanding, balance at beginning of period (in units)	1,457,070	1,576,516
Granted/Issued	324,802	126,239
Forfeited	0	0
Conversions from LTIP units to Other Common Units	165,672	245,685
Redemptions from Other Common Units to common stock	0	0
Units outstanding, balance at end of period (in units)	1,616,200	1,457,070
Other Common Units | Noncontrolling Interest - Unit holders in Operating Partnership
Noncontrolling interest
Units outstanding, balance at beginning of period (in units)	2,639,617	2,057,365
Granted/Issued	0	687,827
Forfeited	0	0
Conversions from LTIP units to Other Common Units	(165,672)	(245,685)
Redemptions from Other Common Units to common stock	352,055	351,260
Units outstanding, balance at end of period (in units)	2,453,234	2,639,617

Noncontrolling Interest - LTIP

Noncontrolling Interest - LTIP FV Assumptions (Details) - LTIP Units - USD ($) $ / shares in Units, $ in Thousands	Mar. 12, 2018	Jan. 05, 2018	Sep. 30, 2018	Dec. 31, 2017
Assumptions
LTIP units at issuance			324,802	126,239
Granted on March 12, 2018
Assumptions
Expected term (years)	10 years
Expected volatility	22.00%
Expected dividend yield	6.00%
Risk-free interest rate	2.46%
Fair value of LTIP units at issuance (in thousands)	$ 90
LTIP units at issuance	3,930
Fair value unit price per LTIP unit at issuance	$ 22.90
Granted on January 5, 2018
Assumptions
Expected term (years)		10 years
Expected volatility		22.00%
Expected dividend yield		6.00%
Risk-free interest rate		2.09%
Fair value of LTIP units at issuance (in thousands)		$ 3,447
LTIP units at issuance		137,616
Fair value unit price per LTIP unit at issuance		$ 25.05
Executive Officer [Member] | Share-based Compensation Award, Tranche One [Member] | Granted on January 5, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)		4 years

Noncontrolling Interest - LTI_2

Noncontrolling Interest - LTIP Units (Details) - LTIP Units - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs	$ 5,700		$ 5,700
Unrecognized compensation costs, period for recognition			2 years 5 months 20 days
Units
Unvested at beginning of period (in shares)			300,307	403,423	403,423
Granted (in shares)			324,802		126,239
Vested (in shares)	(30,949)	(44,942)	(342,940)	(157,816)	(229,355)
Forfeited (in shares)			0		0
Unvested at end of period (in shares)	282,169		282,169		300,307
Fair value of shares vested	$ 851	$ 1,235	$ 9,002	$ 4,146

Equity Incentive Plan - Perform

Equity Incentive Plan - Performance Plan Assumptions (Details) - Performance shares - Awarded in 2018 $ in Thousands	Jan. 05, 2018USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	22.00%
Expected dividend yield	6.00%
Risk-free interest rate	2.09%
Fair value of performance units grant (in thousands)	$ 5,456

Equity Incentive Plan - 2018 Ac

Equity Incentive Plan - 2018 Activity (Details) - USD ($) $ in Thousands	Apr. 30, 2018	Jan. 01, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
LTIP Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value			$ 851	$ 1,235	$ 9,002	$ 4,146
Unrecognized compensation costs			5,700		$ 5,700
Unrecognized compensation costs, period for recognition					2 years 5 months 20 days
Performance shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs			$ 6,100		$ 6,100
Unrecognized compensation costs, period for recognition					2 years 3 months 20 days
Equity Incentive Plan2011 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized	3,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	6,642,461
Outperformance Program2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)		3 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value		$ 6,200
Outperformance Program2015 [Member] | LTIP Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Issued During Period, Shares, Share-based Compensation, Gross		183,256
Outperformance Program2015 [Member] | Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Issued During Period, Shares, Share-based Compensation, Gross		53,722
Stock Repurchased and Retired During Period, Shares		15,183

Equity Incentive Plan - Equity

Equity Incentive Plan - Equity Non-cash Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Common Stock
Equity Incentive Plan
Number of days of average trailing stock price used to calculate number of shares of common stock granted			10 days
General and Administrative Expenses
Equity Incentive Plan
Share-based compensation	$ 2,236	$ 2,384	$ 6,671	$ 7,159
General and Administrative Expenses | Independent Director
Equity Incentive Plan
Share-based compensation	99	87	285	265
General and Administrative Expenses | Restricted stock
Equity Incentive Plan
Share-based compensation	406	594	1,269	1,776
General and Administrative Expenses | LTIP Units
Equity Incentive Plan
Share-based compensation	893	1,167	2,654	3,508
General and Administrative Expenses | Performance shares
Equity Incentive Plan
Share-based compensation	$ 838	$ 536	$ 2,463	$ 1,610

Earnings Per Share (Details)

Earnings Per Share (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Participating securities	193,117	237,207	196,871	238,129

Earnings Per Share - Reconcilia

Earnings Per Share - Reconciliation of Numerator and Denominator (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator
Net income	$ 8,876	$ 21,839	$ 48,989	$ 23,276
Less: preferred stock dividends	1,289	2,449	6,315	7,345
Preferred Stock Redemption Premium	0	0	2,661	0
Less: amount allocated to participating securities	69	84	209	250
Less: income attributable to noncontrolling interest after preferred stock dividends	281	828	1,589	673
Net income attributable to common stockholders	$ 7,237	$ 18,478	$ 38,215	$ 15,008
Denominator
Weighted average common shares outstanding — basic	105,783	92,787	101,095	87,632
Share-based compensation	550	648	400	606
Weighted average common shares outstanding — diluted	106,333	93,435	101,495	88,238
Net income per share — basic and diluted
Net income per share attributable to common stockholders — basic	$ 0.07	$ 0.20	$ 0.38	$ 0.17
Net income per share attributable to common stockholders — diluted	$ 0.07	$ 0.20	$ 0.38	$ 0.17
Restricted stock
Net income per share — basic and diluted
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	193	237	197	238

Commitments and Contingencies -

Commitments and Contingencies - Agreements (Details) $ in Millions	Sep. 30, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
Letters of credit outstanding	$ 5.6