Healthcare Realty Trust 10-K 14 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Jan. 26, 2018	Jun. 30, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	HEALTHCARE REALTY TRUST INC
Entity Central Index Key	899,749
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Common Stock, Shares Outstanding		125,144,327
Entity Public Float			$ 3,878,376,057

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Real estate properties:
Land	$ 201,283	$ 199,672
Buildings, improvements and lease intangibles	3,601,460	3,386,480
Personal property	10,314	10,291
Construction in progress	5,458	11,655
Land held for development	20,123	20,123
Total real estate properties	3,838,638	3,628,221
Less accumulated depreciation	(897,430)	(840,839)
Total real estate properties, net	2,941,208	2,787,382
Cash and cash equivalents	6,215	5,409
Restricted cash	0	49,098
Assets held for sale and discontinued operations, net	33,147	3,092
Other assets, net	213,015	195,666
Total assets	3,193,585	3,040,647
Liabilities:
Notes and bonds payable	1,283,880	1,264,370
Accounts payable and accrued liabilities	70,995	78,266
Liabilities of assets held for sale and discontinued operations	93	614
Other liabilities	48,734	43,983
Total liabilities	1,403,702	1,387,233
Commitments and contingencies
Stockholders' Equity:
Preferred stock, $.01 par value; 50,000 shares authorized; none issued and outstanding	0	0
Common stock, $.01 par value; 300,000 and 150,000 shares authorized; 125,132 and 116,417 shares issued and outstanding at December 31, 2017 and 2016, respectively.	1,251	1,164
Additional paid-in capital	3,173,429	2,917,914
Accumulated other comprehensive loss	(1,299)	(1,401)
Cumulative net income attributable to common stockholders	1,018,348	995,256
Cumulative dividends	(2,401,846)	(2,259,519)
Total stockholders’ equity	1,789,883	1,653,414
Total liabilities and stockholders' equity	$ 3,193,585	$ 3,040,647

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, authorized shares	50,000,000	50,000,000
Preferred stock, issued shares	0	0
Preferred stock, outstanding shares	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares	300,000,000	150,000,000
Common stock, issued shares	125,132,000	116,417,000
Common stock, outstanding shares (shares)	125,132,000	116,417,000

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
REVENUES
Rental income	$ 422,852	$ 407,481	$ 383,333
Mortgage interest			91
Other operating	1,647	4,149	5,047
Total Revenue	424,499	411,630	388,471
EXPENSES
Property operating	157,233	146,458	140,195
General and administrative	32,992	31,309	24,716
Acquisition and pursuit costs	2,180	4,496	2,209
Depreciation and amortization	142,472	127,690	116,614
Bad debt, net of recoveries	169	(21)	(193)
Total Expenses	335,046	309,932	283,541
OTHER INCOME (EXPENSE)
Gain on sales of real estate assets	39,519	41,038	56,602
Interest Expense	(56,402)	(57,351)	(65,534)
Loss on extinguishment of debt	(44,985)		(27,998)
Pension termination		(4)	(5,260)
Impairment of real estate assets	(5,385)		(3,639)
Impairment of internally-developed software			(654)
Interest and other income, net	896	375	389
Total other income (expense)	(66,357)	(15,942)	(46,094)
INCOME FROM CONTINUING OPERATIONS	23,096	85,756	58,836
DISCONTINUED OPERATIONS
Income (loss) from discontinued operations	(9)	(71)	715
Impairments of real estate assets		(121)	(686)
Gain on sales of real estate properties	5	7	10,571
INCOME (LOSS) FROM DISCONTINUED OPERATIONS	(4)	(185)	10,600
NET INCOME	$ 23,092	$ 85,571	$ 69,436
BASIC EARNINGS PER COMMON SHARE:
Income from continuing operations (in dollars per share)	$ 0.18	$ 0.79	$ 0.59
Discontinued operations (in dollars per share)	0	0	0.11
Net income (in dollars per share)	0.18	0.79	0.70
DILUTED EARNINGS PER COMMON SHARE:
Income from continuing operations (in dollars per share)	0.18	0.78	0.59
Discontinued operations (in dollars per share)	0	0	0.11
Net income (in dollars per share)	$ 0.18	$ 0.78	$ 0.70
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING - BASIC (in shares)	117,926,158	108,572,102	99,171,352
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING - DILUTED (in shares)	118,017,165	109,386,997	99,880,302

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
NET INCOME	$ 23,092	$ 85,571	$ 69,436
Other comprehensive income:
Reclassification adjustment for losses included in net income (Pension termination)			2,519
Reclassification adjustment for losses included in net income (Interest expense)	176	168	115
Losses on settlement of swaps arising during the period	(74)		(1,684)
Other comprehensive income	102	168	950
COMPREHENSIVE INCOME	$ 23,194	$ 85,739	$ 70,386

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) $ in Thousands	Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Cumulative Net Income	Cumulative Dividends	Total Stockholders' Equity
Beginning Balance at Dec. 31, 2014	$ 0	$ 988	$ 2,389,830	$ (2,519)	$ 840,249	$ (2,007,494)	$ 1,221,054
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock, net of costs		25	66,886				66,911
Common stock redemption			(1,367)				(1,367)
Stock-based compensation		2	6,027				6,029
Net income					69,436		69,436
Amounts reclassified from accumulated other comprehensive loss arising from loss on defined benefit pension plan				2,519			2,519
Loss on interest rate swaps	0			(1,569)			(1,569)
Dividends to common stockholders ($1.20 per share)						(120,266)	(120,266)
Ending Balance at Dec. 31, 2015	0	1,015	2,461,376	(1,569)	909,685	(2,127,760)	1,242,747
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock, net of costs		140	450,409				450,549
Common stock redemption			(1,460)				(1,460)
Stock-based compensation		9	7,589				7,598
Net income					85,571		85,571
Loss on interest rate swaps		0		168			168
Dividends to common stockholders ($1.20 per share)		0				(131,759)	(131,759)
Ending Balance at Dec. 31, 2016	0	1,164	2,917,914	(1,401)	995,256	(2,259,519)	1,653,414
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock, net of costs		84	248,508				248,592
Common stock redemption		(1)	(3,017)				(3,018)
Stock-based compensation		4	10,024				10,028
Net income					23,092		23,092
Loss on interest rate swaps				102			102
Dividends to common stockholders ($1.20 per share)						(142,327)	(142,327)
Ending Balance at Dec. 31, 2017	$ 0	$ 1,251	$ 3,173,429	$ (1,299)	$ 1,018,348	$ (2,401,846)	$ 1,789,883

Consolidated Statements of Equ7

Consolidated Statements of Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Dividend per share to common stockholders (in dollars per share)	$ 1.20	$ 1.20	$ 1.20
Cumulative Dividends
Dividend per share to common stockholders (in dollars per share)	1.20	1.20	1.20
Total Stockholders' Equity
Dividend per share to common stockholders (in dollars per share)	$ 1.20	$ 1.20	$ 1.20

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Cash Flows [Abstract]
Net income	$ 23,092	$ 85,571	$ 69,436
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	142,472	127,690	116,614
Other amortization	3,879	3,351	3,749
Stock-based compensation	10,028	7,598	6,029
Amortization of straight-line rent receivable	(6,072)	(7,201)	(9,600)
Amortization of straight-line rent liability	1,497	67	771
Gain on sales of real estate assets	(39,524)	(41,044)	(67,229)
Loss on extinguishment of debt	44,985		27,998
Impairment of real estate assets	5,385	121	4,325
Pension termination			5,260
Impairment of internally-developed software			654
Equity income from unconsolidated joint ventures	(7)
Provision for bad debts, net	159	(21)	(194)
Changes in operating assets and liabilities:
Other assets	(2,156)	(1,332)	(2,932)
Accounts payable and accrued liabilities	(7,307)	449	(2,202)
Other liabilities	3,335	(23,977)	1,304
Net cash provided by operating activities	179,766	151,272	153,983
INVESTING ACTIVITIES
Acquisitions of real estate	(274,668)	(224,944)	(154,858)
Development of real estate	(14,911)	(34,719)	(17,354)
Additional long-lived assets	(80,613)	(71,433)	(48,769)
Investment in unconsolidated joint ventures	(8,701)
Proceeds from sales of real estate	119,426	93,253	153,281
Proceeds from mortgages and notes receivable repayments	19	19	1,918
Net cash used in investing activities	(259,448)	(237,824)	(65,782)
FINANCING ACTIVITIES
Net borrowings (repayments) on unsecured credit facility	82,000	(99,000)	121,000
Repayment on term loan		(50,000)
Borrowings of notes and bonds payable	297,459	11,500	249,793
Repayments on notes and bonds payable	(5,829)	(37,910)	(72,724)
Redemption of notes and bonds payable	(442,774)		(326,830)
Dividends paid	(142,327)	(131,759)	(120,266)
Net proceeds from issuance of common stock	248,554	450,503	66,942
Common stock redemptions	(1,686)	(1,756)	(1,367)
Settlement of swaps			(1,684)
Debt issuance and assumption costs	(4,007)	(4,621)	(2,482)
Net cash provided by (used in) financing activities	31,390	136,957	(87,618)
Increase (decrease) in cash, cash equivalents and restricted cash	(48,292)	50,405	583
Cash, cash equivalents and restricted cash at beginning of period	54,507	4,102	3,519
Cash, cash equivalents and restricted cash at end of period	6,215	54,507	4,102
Supplemental Cash Flow Information:
Interest paid	64,395	55,878	69,773
Mortgage notes payable assumed upon acquisition (adjusted to fair value)	46,374	13,951	28,783
Invoices accrued for construction, tenant improvements and other capitalized costs	8,303	11,734	10,431
Capitalized interest	$ 871	$ 1,258	$ 239

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Business Overview Healthcare Realty Trust Incorporated (the “Company”) is a real estate investment trust ("REIT") that owns, leases, manages, acquires, finances, develops and redevelops income-producing real estate properties associated primarily with the delivery of outpatient healthcare services throughout the United States of America. The Company had gross investments of approximately $3.8 billion in 201 real estate properties, construction in progress, land held for development and corporate property as of December 31, 2017 . The Company’s 201 owned real estate properties are located in 27 states and total approximately 14.6 million square feet. The Company provided property management services to approximately 11.5 million square feet nationwide. Square footage and property count disclosures in this Annual Report on Form 10-K are unaudited. Principles of Consolidation The Consolidated Financial Statements include the accounts of the Company, its wholly owned subsidiaries, joint ventures, partnerships and consolidated variable interest entities (“VIE”) where the Company controls the operating activities of the VIE. In accordance with the consolidation accounting standards, the Company must evaluate each contractual relationship it has with its lessees, borrowers, or others to determine whether or not the contractual arrangement creates a variable interest in those entities. If the Company determines that it has a variable interest and the entity is a VIE, then management must determine whether or not the Company is the primary beneficiary of the VIE, resulting in consolidation of the VIE if the Company is the primary beneficiary. A primary beneficiary has the power to direct those activities of the VIE that most significantly impact its economic performance and has the obligation to absorb the losses of, or receive the benefits from, the VIE. The Company had no VIEs as of December 31, 2017 and 2016 . The Company's investments in its unconsolidated joint ventures are included in other assets and the related equity income is recognized in other income (expense) on the Company's Consolidated Financial Statements. See Note 7 for additional information. All significant intercompany accounts, transactions and balances have been eliminated upon consolidation in the Consolidated Financial Statements. Use of Estimates in the Consolidated Financial Statements Preparation of the Consolidated Financial Statements in accordance with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect amounts reported in the Consolidated Financial Statements and accompanying notes. Actual results may differ from those estimates. Segment Reporting The Company owns, leases, acquires, manages, finances, develops and redevelops outpatient and other healthcare-related properties. The Company is managed as one reporting unit, rather than multiple reporting units, for internal reporting purposes and for internal decision-making. Therefore, the Company discloses its operating results in a single reportable segment. Real Estate Properties Real estate properties are recorded at cost or at fair value if acquired in a transaction that is a business combination under Accounting Standards Codification Topic 805, Business Combinations . Cost or fair value at the time of acquisition is allocated among land, buildings, tenant improvements, lease and other intangibles, and personal property as applicable. The Company’s gross real estate assets, on a financial reporting basis, totaled approximately $3.8 billion as of December 31, 2017 and $3.6 billion as of December 31, 2016 . During 2017 and 2016 , the Company eliminated against accumulated depreciation approximately $10.2 million and $6.7 million , respectively, of fully amortized real estate intangibles that were initially recorded as a component of certain real estate acquisitions. Also during 2017 and 2016 , approximately $2.6 million and $0.1 million of fully depreciated tenant and capital improvements that were no longer in service were eliminated against accumulated depreciation. Depreciation expense for the three years ended December 31, 2017, 2016 and 2015 was $129.4 million , $116.5 million and $106.5 million , respectively. Depreciation and amortization of real estate assets and liabilities in place as of December 31, 2017 , is provided for on a straight-line basis over the asset’s estimated useful life: Land improvements 5.0 to 39.0 years Buildings and improvements 3.3 to 39.0 years Lease intangibles (including ground lease intangibles) 2.1 to 99.0 years Personal property 2.8 to 20.0 years The Company capitalizes direct costs, including costs such as construction costs and professional services, and indirect costs, including capitalized interest and overhead costs, associated with the development and construction of real estate assets while substantive activities are ongoing to prepare the assets for their intended use. Capitalized interest cost is calculated using the weighted average interest rate of the Company's unsecured debt or the interest rate on project specific debt, if applicable. The Company continues to capitalize interest on the unoccupied portion of the properties in stabilization for up to one year after the buildings have been placed into service, at which time the capitalization of interest must cease. Land Held for Development Land held for development includes parcels of land owned by the Company, upon which the Company intends to develop and own outpatient healthcare facilities. The Company’s investment in six parcels of land held for development located adjacent to certain of the Company's existing medical office buildings in Texas, Iowa and Tennessee totaled approximately $20.1 million as of December 31, 2017 and 2016 . Asset Impairment The Company assesses the potential for impairment of identifiable, definite-lived, intangible assets and long-lived assets, including real estate properties, whenever events occur or a change in circumstances indicates that the carrying value might not be fully recoverable. Indicators of impairment may include significant underperformance of an asset relative to historical or expected operating results; significant changes in the Company’s use of assets or the strategy for its overall business; plans to sell an asset before its depreciable life has ended; the expiration of a significant portion of leases in a property; or significant negative economic trends or negative industry trends for the Company or its operators. In addition, the Company reviews for possible impairment, those assets subject to purchase options and those impacted by casualties, such as tornadoes and hurricanes. If management determines that the carrying value of the Company’s assets may not be fully recoverable based on the existence of any of the factors above, or others, management would measure and record an impairment charge based on the estimated fair value of the property or the estimated fair value less costs to sell the property. Acquisitions of Real Estate Properties with In-Place Leases Acquisitions of real estate properties with in-place leases are accounted for at relative fair value. When a building with in-place leases is acquired, the cost of the acquisition must be allocated between the tangible real estate assets "as-if-vacant" and the intangible real estate assets related to in-place leases based on their estimated fair values. Where appropriate, the intangible assets recorded could include goodwill or customer relationship assets. The values related to above- or below-market in-place lease intangibles are amortized over the remaining term of the leases upon acquisition to rental income where the Company is the lessor and to property operating expense where the Company is the lessee, and are amortized over the remaining term of the leases upon acquisition. The Company considers whether any of the in-place lease rental rates are above- or below-market. An asset (if the actual rental rate is above-market) or a liability (if the actual rental rate is below-market) is calculated and recorded in an amount equal to the present value of the future cash flows that represent the difference between the actual lease rate and the average market rate. If an in-place lease is identified as a below-market rental rate, the Company would also evaluate any renewal options associated with that lease to determine if the intangible should include those periods. The Company also estimates an absorption period, which can vary by property, assuming the building is vacant and must be leased up to the actual level of occupancy when acquired. During that absorption period, the owner would incur direct costs, such as tenant improvements, and would suffer lost rental income. Likewise, the owner would have acquired a measurable asset in that, assuming the building was vacant, certain fixed costs would be avoided because the actual in-place lessees would reimburse a certain portion of fixed costs through expense reimbursements during the absorption period. All of these intangible assets (above- or below-market lease, tenant improvement costs avoided, leasing costs avoided, rental income lost, and expenses recovered through in-place lessee reimbursements) are estimated and recorded in amounts equal to the present value of estimated future cash flows. The actual purchase price is allocated based on the various asset fair values described above. The building and tenant improvement components of the purchase price are depreciated over the estimated useful life of the building or the weighted average remaining term of the in-places leases. The at-market, in-place lease intangibles are amortized to amortization expense over the weighted average remaining term of the leases, customer relationship assets are amortized to amortization expense over terms applicable to each acquisition, and any goodwill recorded would be reviewed for impairment at least annually. The fair values of at-market in-place lease and other intangible assets are amortized and reflected in amortization expense in the Company’s Consolidated Statements of Income. See Note 8 for more details on the Company’s intangible assets. Fair Value Measurements Fair value is defined as the price that would be received to sell an asset, or paid to transfer a liability, in an orderly transaction between market participants. In calculating fair value, a company must maximize the use of observable market inputs, minimize the use of unobservable market inputs and disclose in the form of an outlined hierarchy the details of such fair value measurements. A hierarchy of valuation techniques is defined to determine whether the inputs to a fair value measurement are considered to be observable or unobservable in a marketplace. Observable inputs reflect market data obtained from independent sources, while unobservable inputs reflect the Company’s market assumptions. This hierarchy requires the use of observable market data when available. These inputs have created the following fair value hierarchy: • Level 1 – quoted prices for identical instruments in active markets; • Level 2 – quoted prices for similar instruments in active markets; quoted prices for identical or similar instruments in markets that are not active; and model-derived valuations in which significant inputs and significant value drivers are observable in active markets; and • Level 3 – fair value measurements derived from valuation techniques in which one or more significant inputs or significant value drivers are unobservable. Executed purchase and sale agreements, that are binding agreements, are categorized as level one inputs. Brokerage estimates, letters of intent, or unexecuted purchase and sale agreements are considered to be level three as they are nonbinding in nature. During 2017 , in connection with the sale of a medical office building, the Company recorded an impairment charge in continuing operations of approximately $5.1 million based on the contractual sales price, a level one input. The Company used level one inputs to record an impairment charge in continuing operations of approximately $0.3 million related to another property sold during 2017, reducing the Company's carrying value to the estimated fair value of the property less costs to sell prior to sale. Fair Value of Derivative Financial Instruments Derivative financial instruments are recorded at fair value on the Company's Consolidated Balance Sheets as other assets or other liabilities. The valuation of derivative instruments requires the Company to make estimates and judgments that affect the fair value of the instruments. Fair values of derivatives are estimated by pricing models that consider the forward yield curves and discount rates. The fair value of the Company's forward starting interest rate swap contracts are estimated by pricing models that consider foreign trade rates and discount rates. Such amounts and the recognition of such amounts are subject to significant estimates that may change in the future. For derivatives designated in qualifying cash flow hedging relationships, the change in fair value of the effective portion of the derivatives is recognized in accumulated other comprehensive income (loss). Gains and losses are reclassified from accumulated other comprehensive income (loss) into earnings once the underlying hedged transaction is recognized in earnings. As of December 31, 2017 and 2016, the Company had $1.3 million and $1.4 million , respectively recorded in accumulated other comprehensive loss related to forward starting interest rate swaps entered into and settled during 2015 and a hedge of the Company's variable rate debt. See Note 10 for additional information. Cash, Cash Equivalents and Restricted Cash Cash and cash equivalents includes short-term investments with original maturities of three months or less when purchased. Restricted cash includes cash held in escrow in connection with proceeds from the sales of certain real estate properties. The carrying amount approximates fair value due to the short term maturity of these investments. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Company's Consolidated Balance Sheets with the same amounts shown on the Company's Consolidated Statements of Cash Flows: December 31, (Dollars in thousands) 2017 2016 Cash and cash equivalents $ 6,215 $ 5,409 Restricted cash — 49,098 Total cash, cash equivalents and restricted cash $ 6,215 $ 54,507 Allowance for Doubtful Accounts and Credit Losses Accounts Receivable Management monitors the aging and collectibility of its accounts receivable balances on an ongoing basis. Whenever deterioration in the timeliness of payment from a tenant or sponsoring health system is noted, management investigates and determines the reason or reasons for the delay. Considering all information gathered, management’s judgment is exercised in determining whether a receivable is potentially uncollectible and, if so, how much or what percentage may be uncollectible. Among the factors management considers in determining collectibility are: the type of contractual arrangement under which the receivable was recorded (e.g., a triple net lease, a gross lease, a property operating agreement, or some other type of agreement); the tenant’s reason for slow payment; industry influences under which the tenant operates; evidence of willingness and ability of the tenant to pay the receivable; credit-worthiness of the tenant; collateral, security deposit, letters of credit or other monies held as security; tenant’s historical payment pattern; other contractual agreements between the tenant and the Company; relationship between the tenant and the Company; the state in which the tenant operates; and the existence of a guarantor and the willingness and ability of the guarantor to pay the receivable. Considering these factors and others, management concludes whether all or some of the aged receivable balance is likely uncollectible. Upon determining that some portion of the receivable is likely uncollectible, the Company records a provision for bad debts for the amount it expects will be uncollectible. When efforts to collect a receivable are exhausted, the receivable amount is charged off against the allowance. The Company does not hold any accounts receivable for sale. Mortgage Notes The Company had no mortgage notes receivable outstanding as of December 31, 2017 and 2016 and no allowances were recorded on mortgage notes receivables during 2017 or 2016 . The Company evaluates collectibility of any mortgage notes and records allowances on the notes as necessary. A loan is impaired when it is probable that a creditor will be unable to collect all amounts due according to the contractual terms of the loan as scheduled, including both contractual interest and principal payments. This assessment also includes an evaluation of the loan collateral. If a mortgage loan becomes past due, the Company will review the specific circumstances and may discontinue the accrual of interest on the loan. The loan is not returned to accrual status until the debtor has demonstrated the ability to continue debt service in accordance with the contractual terms. Loans placed on non-accrual status will be accounted for either on a cash basis, in which income is recognized only upon receipt of cash, or on a cost-recovery basis, in which all cash receipts reduce the carrying value of the loan, based on the Company’s expectation of future collectibility. Goodwill and Other Intangible Assets Goodwill and intangible assets with indefinite lives are not amortized, but are tested at least annually for impairment. Intangible assets with finite lives are amortized over their respective lives to their estimated residual values and are reviewed for impairment only when impairment indicators are present. Identifiable intangible assets of the Company are comprised of enterprise goodwill, in-place lease intangible assets, customer relationship intangible assets, and deferred financing costs. In-place lease and customer relationship intangible assets are amortized on a straight-line basis over the applicable lives of the assets. Deferred financing costs are amortized over the term of the related credit facility or other debt instrument under the straight-line method, which approximates amortization under the effective interest method. Goodwill is not amortized but is evaluated annually as of December 31 for impairment. Both the 2017 and 2016 impairment evaluations indicated that no impairment had occurred with respect to the $3.5 million goodwill asset. See Note 8 for more detail on the Company’s intangible assets. Contingent Liabilities From time to time, the Company may be subject to loss contingencies arising from legal proceedings and similar matters. Additionally, while the Company maintains comprehensive liability and property insurance with respect to each of its properties, the Company may be exposed to unforeseen losses related to uninsured or underinsured damages. The Company continually monitors any matters that may present a contingent liability, and, on a quarterly basis, management reviews the Company’s reserves and accruals in relation to each of them, adjusting provisions as necessary in view of changes in available information. Liabilities for contingencies are first recorded when a loss is determined to be both probable and can be reasonably estimated. Changes in estimates regarding the exposure to a contingent loss are reflected as adjustments to the related liability in the periods when they occur. Because of uncertainties inherent in the estimation of contingent liabilities, it is possible that the Company’s provision for contingent losses could change materially in the near term. To the extent that any significant losses, in addition to amounts recognized, are at least reasonably possible, such amounts will be disclosed in the notes to the Consolidated Financial Statements. Stock-Based Compensation The Company has various employee and director stock-based awards outstanding. These awards include non-vested common stock and options to purchase common stock granted to employees pursuant to the 2015 Stock Incentive Plan and its predecessor plans (the “2015 Incentive Plan”) and the 2000 Employee Stock Purchase Plan (the “Employee Stock Purchase Plan”). The Company recognizes share-based payments to employees and directors in the Consolidated Statements of Income on a straight-line basis over the requisite service period based on the fair value of the award on the measurement date. The Employee Stock Purchase Plan features a “look-back” provision which enables the employee to purchase a fixed number of common shares at the lesser of 85% of the market price on the date of grant or 85% of the market price on the date of exercise, with optional purchase dates occurring once each quarter for 27 months . The Company accounts for awards to its employees under the Employee Stock Purchase Plan based on fair value, using the Black-Scholes model, and generally recognizes expense over the award’s vesting period, net of estimated forfeitures. Since the options granted under the Employee Stock Purchase Plan immediately vest, the Company records compensation expense for those options when they are granted in the first quarter of each year and then may record additional compensation expense in subsequent quarters as warranted. In each of the years ended December 31, 2017 , 2016 and 2015 , the Company recognized in general and administrative expenses approximately $0.2 million of compensation expense related to the annual grant of options to its employees to purchase shares under the Employee Stock Purchase Plan. See Note 13 for details on the Company’s stock-based awards. Accumulated Other Comprehensive Income (Loss) Certain items must be included in comprehensive income, including items such as foreign currency translation adjustments, minimum pension liability adjustments, derivative instruments and unrealized gains or losses on available-for-sale securities. The Company’s accumulated other comprehensive income (loss) as of December 31, 2017 consists of the loss for changes in the fair value of active derivatives designated as cash flow hedges and the loss on the unamortized settlement of four forward starting swaps. As of December 31, 2016, the Company's accumulated other comprehensive income (loss) consisted only of the loss on the unamortized settlement of four forward starting swaps. See Note 10 for more details on the Company's derivative financial instruments. Revenue Recognition The Company recognizes revenue when it is realized or realizable and earned. There are four criteria that must all be met before a Company may recognize revenue, including that persuasive evidence that an arrangement exists, delivery has occurred or services have been rendered (i.e., the tenant has taken possession of and controls the physical use of the leased asset), the price has been fixed or is determinable, and collectibility is reasonably assured. Income received but not yet earned is deferred until such time it is earned. Deferred revenue, included in other liabilities on the Consolidated Balance Sheets, was $36.0 million and $32.4 million , respectively, as of December 31, 2017 and 2016 which includes deferred tenant improvement reimbursements of $20.1 million and $20.6 million , respectively, which will be recognized as revenue over the life of each respective lease. The Company derives most of its revenues from its real estate property portfolio. The Company’s rental and mortgage interest income is recognized based on contractual arrangements with its tenants, sponsoring health systems or borrowers. These contractual arrangements fall into three categories: leases, mortgage notes receivable, and property operating agreements as described in the following paragraphs. The Company may accrue late fees based on the contractual terms of a lease or note. Such fees, if accrued, are included in rental income or mortgage interest income on the Company’s Consolidated Statements of Income, based on the type of contractual agreement. Rental Income Rental income related to non-cancelable operating leases is recognized as earned over the life of the lease agreements on a straight-line basis. The Company's lease agreements generally include provisions for stated annual increases or increases based on a Consumer Price Index ("CPI"). Rental income from properties under multi-tenant office lease arrangements and rental income from properties with single-tenant lease arrangements are included in rental income on the Company's Consolidated Statements of Income. The components of rental income are as follows: Year Ended December 31, (Dollars in thousands) 2017 2016 2015 Property operating income $ 363,907 $ 336,409 $ 306,550 Single-tenant net lease 52,873 63,871 67,238 Straight-line rent 6,072 7,201 9,545 Rental income $ 422,852 $ 407,481 $ 383,333 Operating expense recoveries, included in property operating income, were approximately $73.4 million , $66.0 million and $58.9 million , respectively, for the years ended December 31, 2017 , 2016 and 2015 . Mortgage Interest Income Interest income on the Company’s mortgage notes receivable is recognized based on the interest rates, maturity dates and amortization periods in accordance with each note agreement. The Company has no outstanding mortgage notes receivable as of December 31, 2017 , 2016 and 2015. The Company amortizes any fees paid related to its mortgage notes receivable to mortgage interest income over the term of the loan on a straight-line basis which approximates amortization under the effective interest method. Other Operating Income Other operating income on the Company’s Consolidated Statements of Income was comprised of the following: Year Ended December 31, (Dollars in thousands) 2017 2016 2015 Property lease guaranty revenue $ 726 $ 3,058 $ 3,890 Interest income 361 473 579 Management fee income 276 369 370 Other 284 249 208 $ 1,647 $ 4,149 $ 5,047 One , two and five of the Company’s owned real estate properties as of December 31, 2017 , 2016 and 2015, respectively, were covered under property operating agreements between the Company and a sponsoring health system, which contractually obligate the sponsoring health system to provide to the Company a minimum return on the Company’s investment in the property in exchange for the right to be involved in the operating decisions of the property, including tenancy. If the minimum return is not achieved through normal operations of the property, the Company calculates and accrues to property lease guaranty revenue, each quarter, any shortfalls due from the sponsoring health systems under the terms of the property operating agreement. Interest income generally relates to interest on tenant improvement reimbursements as defined in each note or lease agreement. Management fees for property management services provided to third parties are generally calculated, accrued and billed monthly based on a percentage of cash collections of tenant receivables for the month or a stated amount per square foot. Internal management fee income, where the Company manages its owned properties, is eliminated in consolidation. Federal Income Taxes No provision has been made for federal income taxes. The Company intends at all times to qualify as a REIT under Sections 856 through 860 of the Internal Revenue Code. The Company must distribute at least 90% per annum of its real estate investment trust taxable income to its stockholders and meet other requirements to continue to qualify as a real estate investment trust. See Note 16 for further discussion. The Company classifies interest and penalties related to uncertain tax positions, if any, in the Consolidated Financial Statements as a component of general and administrative expenses. No such amounts were recognized during the three years ended December 31, 2017. Federal tax returns for the years 2014, 2015 , 2016 and 2017 are currently subject to examination by taxing authorities. State Income Taxes The Company must pay certain state income taxes and the provisions for such taxes are generally included in general and administrative expense on the Company’s Consolidated Statements of Income. See Note 16 for further discussion. Sales and Use Taxes The Company must pay sales and use taxes to certain state tax authorities based on rents collected from tenants in properties located in those states. The Company is generally reimbursed for these taxes by the tenant. The Company accounts for the payments to the taxing authority and subsequent reimbursement from the tenant on a net basis in revenues in the Company’s Consolidated Statements of Income. Discontinued Operations The Company sells properties from time to time due to a variety of factors, including among other things, market conditions or the exercise of purchase options by tenants. The Company does not expect these dispositions to meet the amended definition of a discontinued operation as defined in Accounting Standards Update ("ASU") No. 2014-08, "Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity." The Company adopted ASU No. 2014-08 on a prospective basis beginning January 1, 2015 which excluded properties previously in discontinued operations prior to adoption. However, if a sale were to meet the amended definition representing a strategic shift that has or will have a major effect on the Company's operations and financial results, the operating results of the properties that have been sold or are held for sale will be reported as discontinued operations in the Company’s Consolidated Statements of Income for all periods presented. Assets Held for Sale Long-lived assets held for sale are reported at the lower of their carrying amount or their fair value less cost to sell estimate. Further, depreciation of these assets ceases at the time the assets are classified as held for sale. Losses resulting from the sale of such properties are characterized as impairment losses in the Consolidated Statements of Income. See Note 5 for more detail on discontinued operations and assets held for sale. Earnings per Share The Company uses the two-class method of computing net earnings per common share. Earnings per common share is calculated by considering share-based payment awards that contain nonforfeitable rights to dividends or dividend equivalents as participating securities. Undistributed earnings (excess net income over dividend payments) are allocated on a prorata basis to common shareholders and restricted shareholders. Undistributed losses (dividends in excess of net income) do not get allocated to restricted stockholders as they do not have the contractual obligation to share in losses. The amount of undistributed losses that applies to the restricted stockholders is allocated to the common stockholder. Basic earnings per common share is calculated using weighted average shares outstanding less issued and outstanding non-vested shares of common stock. Diluted earnings per common share is calculated using weighted average shares outstanding plus the dilutive effect of the outstanding stock options from the Employee Stock Purchase Plan using the treasury stock method and the average stock price during the period. See Note 14 for the calculations of earnings per share. Reclassifications Condensed Consolidated Statements of Income Certain reclassifications have been made on the Company's Condensed Consolidated Statements of Income. The Company reclassified acquisition and pursuit costs from the general and administrative line item to a separate line item. The acquisition and pursuit costs line item includes direct third party and travel costs related to the Company's pursuit of acquisitions and developments. In addition, the Company combined the line items labeled depreciation and amortization into one line item. These reclassifications are as follows: Year Ended December 31, 2016 2015 (in thousands) As Previously Reported As Reclassified As Previously Reported As Reclassified General and administrative $ 35,805 $ 31,309 $ 26,925 $ 24,716 Acquisition and pursuit costs — 4,496 — 2,209 Total $ 35,805 $ 35,805 $ 26,925 $ 26,925 Depreciation $ 116,483 $ — $ 106,530 $ — Amortization 11,207 — 10,084 — Depreciation and amortization — 127,690 — 116,614 Total $ 127,690 $ 127,690 $ 116,614 $ 116,614 New A

Property Investments

Property Investments	12 Months Ended
	Dec. 31, 2017
Real Estate Investment Property, Net [Abstract]
Property Investments	Property Investments The Company invests in healthcare-related properties located throughout the United States. The Company provides management, leasing, development and redevelopment services, and capital for the construction of new facilities as well as for the acquisition of existing properties. The Company had gross investments of approximately $3.8 billion in 201 real estate properties, land held for development and corporate property as of December 31, 2017 . The following table summarizes the Company’s investments at December 31, 2017. (Dollars in thousands) Number of Facilities Land Buildings, Improvements,and Lease Intangibles Personal Property Total Accumulated Depreciation Medical office/outpatient: Seattle, Washington 17 $ 24,560 $ 403,614 $ 378 $ 428,552 $ (52,457 ) Dallas, Texas 24 12,472 365,657 416 378,545 (128,557 ) Atlanta, Georgia 8 1,015 187,042 — 188,057 (1,203 ) Los Angeles, California 11 27,709 141,681 277 169,667 (71,808 ) Charlotte, North Carolina 16 4,200 163,603 95 167,898 (56,355 ) Nashville, Tennessee 5 3,143 149,859 278 153,280 (43,000 ) Richmond, Virginia 7 — 146,176 98 146,274 (32,299 ) Honolulu, Hawaii 3 8,327 132,847 159 141,333 (30,066 ) Denver, Colorado 6 4,086 122,689 271 127,046 (18,736 ) San Francisco, California 3 14,054 103,938 43 118,035 (12,223 ) Oklahoma City, Oklahoma 2 7,673 101,432 6 109,111 (10,890 ) Washington, D.C. 4 — 100,570 — 100,570 (15,826 ) Austin, Texas 4 12,756 85,961 105 98,822 (17,498 ) San Antonio, Texas 7 6,647 88,129 370 95,146 (34,514 ) Memphis, Tennessee 7 5,241 88,517 160 93,918 (31,675 ) Des Moines, Iowa 6 12,665 79,214 94 91,973 (18,263 ) Chicago, Illinois 3 5,859 79,295 200 85,354 (15,476 ) Indianapolis, Indiana 3 3,299 71,641 — 74,940 (18,742 ) Other (22 markets) 52 38,598 678,196 1,163 717,957 (206,844 ) 188 192,304 3,290,061 4,113 3,486,478 (816,432 ) Inpatient: Springfield, Missouri 1 1,989 109,304 — 111,293 (12,046 ) Dallas, Texas 1 4,442 92,990 — 97,432 (19,538 ) Erie, Pennsylvania 1 — 21,355 — 21,355 (15,152 ) Los Angeles, California 1 — 12,688 — 12,688 (7,606 ) Denver, Colorado 1 623 10,788 — 11,411 (1,781 ) 5 7,054 247,125 — 254,179 (56,123 ) Other: Des Moines, Iowa 1 — 40,354 5 40,359 (7,704 ) Johnson City, Tennessee 1 253 7,319 408 7,980 (2,798 ) Austin, Texas 1 1,480 3,872 2 5,354 (164 ) Fenton, Michigan 1 40 3,468 32 3,540 (2,738 ) Ovid, Michigan 1 62 3,188 49 3,299 (2,096 ) Fremont, Michigan 1 7 3,242 35 3,284 (2,565 ) St. Louis, Michigan 1 31 1,735 33 1,799 (1,341 ) Detroit, Michigan 1 52 1,096 34 1,182 (829 ) 8 1,925 64,274 598 66,797 (20,235 ) Land Held for Development — 20,123 — — 20,123 (239 ) Construction in Progress — — 5,458 — 5,458 — Corporate Property — — — 5,603 5,603 (4,401 ) — 20,123 5,458 5,603 31,184 (4,640 ) Total real estate investments 201 $ 221,406 $ 3,606,918 $ 10,314 $ 3,838,638 $ (897,430 )

Real Estate Leases

Real Estate Leases	12 Months Ended
	Dec. 31, 2017
Leases [Abstract]
Real Estate Leases	Real Estate Leases Real Estate Leases The Company’s properties are generally leased pursuant to non-cancelable, fixed-term operating leases with expiration dates through 2036 . Some leases and financial arrangements provide for fixed rent renewal terms in addition to market rent renewal terms. Some leases provide the lessee, during the term of the lease and for a short period thereafter, with an option or a right of first refusal to purchase the leased property. The Company’s portfolio of single-tenant net leases generally requires the lessee to pay minimum rent and all taxes (including property tax), insurance, maintenance and other operating costs associated with the leased property. Future minimum lease payments under the non-cancelable operating leases and guaranteed amounts payable to the Company under property operating agreements as of December 31, 2017 are as follows (in thousands): 2018 $ 330,526 2019 282,910 2020 236,454 2021 196,346 2022 168,183 2023 and thereafter 544,677 $ 1,759,096 Revenue Concentrations The Company’s real estate portfolio is leased to a diverse tenant base. The Company's largest revenue concentration is with Baylor Scott & White Health and its affiliates which accounted for 9.7% , 9.8% and 9.8% of the Company's consolidated revenues for the years ended December 31, 2017 , 2016 and 2015 , respectively. Purchase Option Provisions Certain of the Company’s leases include purchase option provisions. The provisions vary by agreement but generally allow the lessee to purchase the property covered by the agreement at fair market value or an amount equal to the Company’s gross investment . The Company expects that the purchase price from its purchase options will be greater than its net investment in the properties at the time of potential exercise by the lessee. The Company had approximately $95.2 million in four real estate properties as of December 31, 2017 that were subject to purchase options that were exercisable.

Acquisitions, Dispositions and

Acquisitions, Dispositions and Mortgage Repayments	12 Months Ended
	Dec. 31, 2017
Acquisitions and Dispositions and Mortgage Repayments [Abstract]
Acquisitions, Dispositions and Mortgage Repayments	Acquisitions, Dispositions and Mortgage Repayments 2017 Real Estate Acquisitions The following table details the Company's acquisitions for the year ended December 31, 2017 : (Dollars in millions) Type (1) Date Purchase Price Mortgage (2) Cash (3) Real Other (4) Square (Unaudited) Real estate acquisitions St. Paul, Minnesota MOB 3/6/17 $ 13.5 $ — $ 13.5 $ 13.3 $ 0.2 34,608 San Francisco, California MOB 6/12/17 26.8 — 26.8 26.8 — 75,649 Washington, D.C. MOB 6/13/17 24.0 (12.1 ) 12.5 24.8 (0.2 ) 62,379 Los Angeles, California MOB 7/31/17 16.3 — 16.7 16.9 (0.2 ) 42,780 Atlanta, Georgia MOB 11/1/17 25.5 — 25.5 26.3 (0.8 ) 76,944 Atlanta, Georgia MOB 11/1/17 30.3 — 30.7 30.7 — 74,024 Atlanta, Georgia (5) MOB 11/1/17 49.7 — 50.9 47.5 3.4 118,180 Atlanta, Georgia MOB 11/1/17 6.7 — 6.7 6.7 — 19,732 Seattle, Washington MOB 11/1/17 12.7 — 12.6 12.8 (0.2 ) 26,345 Atlanta, Georgia (5) MOB 12/13/17 25.8 (10.5 ) 15.3 22.0 3.8 59,427 Atlanta, Georgia MOB 12/13/17 15.4 (4.7 ) 10.8 15.7 (0.2 ) 40,171 Atlanta, Georgia (5) MOB 12/18/17 26.3 (11.8 ) 14.5 24.6 1.7 66,984 Atlanta, Georgia MOB 12/18/17 14.2 (6.7 ) 7.6 14.5 (0.2 ) 40,324 Chicago, Illinois MOB 12/18/17 28.7 — 27.7 28.5 (0.8 ) 99,526 Seattle, Washington MOB 12/18/17 8.8 — 8.8 9.0 (0.2 ) 32,828 Austin, Texas (6) MOB 12/21/17 2.5 — 2.5 2.5 — 7,972 $ 327.2 $ (45.8 ) $ 283.1 $ 322.6 $ 6.3 877,873 ______ (1) MOB = medical office building (2) The mortgage notes payable assumed in the acquisitions do not reflect the fair value adjustments totaling $0.6 million in aggregate recorded by the Company upon acquisition (included in Other). (3) Cash consideration excludes prorations of revenue and expense due to/from seller at the time of the acquisition. (4) Includes other assets acquired, liabilities assumed, intangibles recognized at acquisition and fair value adjustments on debt assumed. (5) The "Other" column includes the equity investment in limited liability companies that own two parking garages. (6) The Company acquired additional ownership interests in an existing building bringing the Company's ownership to 69.4% . The following table summarizes the estimated relative fair values of the assets acquired and liabilities assumed in the real estate acquisitions for 2017 as of the acquisition date: Estimated Fair Value Estimated Useful Life (In millions) (In years) Building $ 272.1 15.0-37.0 Land 11.7 — Land Improvements 1.6 5.0-12.0 Intangibles: At-market lease intangibles 37.2 2.1-12.6 Below-market lease intangibles (0.9 ) 8.5-15.0 Below-market ground lease intangibles 0.4 36.8-99.0 Total intangibles 36.7 Mortgage notes payable assumed, including fair value adjustments (46.4 ) Other assets acquired 0.4 Equity investment in joint ventures 8.7 Accounts payable, accrued liabilities and other liabilities assumed (1.7 ) Total cash paid $ 283.1 2016 Real Estate Acquisitions The following table details the Company's acquisitions for the year ended December 31, 2016 : (Dollars in millions) Type (1) Date Purchase Price Mortgage (2) Cash (3) Real Other (4) Square (unaudited) Real estate acquisitions Seattle, Washington MOB 3/31/16 $ 38.3 $ — $ 37.7 $ 37.7 $ — 69,712 Seattle, Washington MOB 4/29/16 21.6 — 18.8 20.1 (1.3 ) 46,637 Los Angeles, California MOB 5/13/16 20.0 (13.2 ) 6.5 20.4 (0.7 ) 63,012 Seattle, Washington MOB 9/12/16 53.1 — 53.0 54.6 (1.6 ) 87,462 Washington, D.C. (5) MOB 9/26/16 45.2 — 45.1 43.7 1.4 103,783 Baltimore, Maryland (6) MOB 10/11/16 36.2 — 36.4 36.4 — 113,631 Seattle, Washington MOB 10/17/16 9.8 — 9.8 9.9 (0.1 ) 29,753 Seattle, Washington MOB 12/21/16 5.1 — 5.1 5.2 (0.1 ) 20,740 St. Paul, Minnesota MOB 12/21/16 12.6 — 12.5 11.3 1.2 48,281 $ 241.9 $ (13.2 ) $ 224.9 $ 239.3 $ (1.2 ) 583,011 ______ (1) MOB = medical office building (2) The mortgage notes payable assumed in the acquisitions do not reflect the fair value adjustments totaling $0.8 million recorded by the Company upon acquisition (included in Other). (3) Excludes prorations of revenue and expense due to/from seller at the time of the acquisition. (4) Includes other assets acquired, liabilities assumed, intangibles recognized at acquisition and fair value adjustments on debt assumed. (5) A director of the Company serves as the Chief Executive Officer of the Inova Health System. As part of this transaction, the Company assumed a ground lease and tenant leases with Loudon Hospital Center, an affiliate of Inova Health System. (6) Includes two properties. The following table summarizes the estimated relative fair values of the assets acquired and liabilities assumed in the real estate acquisitions for 2016 as of the acquisition date: Estimated Fair Value Estimated Useful Life (In millions) (In years) Building $ 216.8 20.0-35.0 Land 9.7 — Intangibles: At-market lease intangibles 12.8 2.7-10.3 Above-market lease intangibles 0.9 0.7-3.8 Below-market lease intangibles (0.4 ) 1.4-9.4 Above-market ground lease intangibles (1.6 ) 99.0 Below-market ground lease intangibles 2.0 36.8-99.0 Total intangibles 13.7 Mortgage notes payable assumed, including fair value adjustments (14.0 ) Other assets acquired 0.5 Accounts payable, accrued liabilities and other liabilities assumed (1.8 ) Total cash paid $ 224.9 2017 Real Estate Asset Dispositions The following table details the Company's dispositions for the year ended December 31, 2017 : (Dollars in millions) Type (1) Date Sales Price Closing Adjustments Net Net Real Other (3) Gain/ Square Unaudited ) Real estate dispositions Evansville, Indiana OTH 3/6/17 $ 6.4 $ — $ 6.4 $ 1.1 $ — $ 5.3 29,500 Columbus, Georgia (2) MOB 3/7/17 0.6 — 0.6 0.6 — — 12,000 Las Vegas, Nevada (2) MOB 3/30/17 5.5 (0.7 ) 4.8 2.2 0.3 2.3 18,147 Texas (3 properties) IRF 3/31/17 69.5 (1.6 ) 67.9 46.9 5.2 15.8 169,722 Chicago, Illinois (4) MOB 6/16/17 0.5 (0.1 ) 0.4 0.4 — — 5,100 San Antonio, Texas IRF 6/29/17 14.5 (0.2 ) 14.3 5.1 0.9 8.3 39,786 Roseburg, Oregon MOB 6/29/17 23.2 (0.6 ) 22.6 14.5 0.3 7.8 62,246 St. Louis, Missouri MOB 9/7/17 2.5 (0.1 ) 2.4 7.4 0.1 (5.1 ) 79,980 Total dispositions $ 122.7 $ (3.3 ) $ 119.4 $ 78.2 $ 6.8 $ 34.4 416,481 ______ (1) MOB = medical office building; IRF = inpatient rehabilitation facility; OTH = other (2) Previously classified as held for sale. (3) Includes straight-line rent receivables, leasing commissions and lease inducements. (4) The Company recorded an impairment of approximately $0.3 million in the first quarter of 2017 upon management's decision to sell. 2016 Real Estate Asset Dispositions The following table details the Company's dispositions for the year ended December 31, 2016 : (Dollars in millions) Type (1) Date Sales Price Closing Adjustments Net Net Real Other (2) Gain Square Unaudited ) Real estate dispositions Kansas City, Kansas MOB 10/14/16 $ 15.1 $ — $ 15.1 $ 7.2 $ 0.3 $ 7.6 70,908 Nashville, Tennessee MOB 10/28/16 8.8 (0.2 ) 8.6 6.3 0.2 2.1 45,274 Altoona, Pennsylvania IRF 12/20/16 21.5 (0.4 ) 21.1 12.4 0.6 8.1 64,032 Harrisburg, Pennsylvania IRF 12/20/16 24.2 (0.6 ) 23.6 8.2 0.4 15.0 79,836 Phoenix, Arizona IRF 12/20/16 22.3 — 22.3 13.5 1.4 7.4 51,903 Atlanta, Georgia MOB 12/22/16 2.8 (0.2 ) 2.6 1.8 — 0.8 8,749 Total dispositions $ 94.7 $ (1.4 ) $ 93.3 $ 49.4 $ 2.9 $ 41.0 320,702 ______ (1) MOB = medical office building; IRF = inpatient rehabilitation facility (2) Includes straight-line rent receivables, leasing commissions and lease inducements. Potential Dispositions In October 2017, the Company received notice that a tenant is exercising a purchase option on seven properties, comprised of five single-tenant net leased buildings and two multi-tenanted buildings, covered by one purchase option with a stated purchase price of approximately $45.5 million , subject to certain contractual adjustments. The Company's aggregate net book value for these properties, which were classified as held for sale upon receiving notice of the purchase option exercise, was $23.9 million at December 31, 2017 .

Held for Sale and Discontinued

Held for Sale and Discontinued Operations	12 Months Ended
	Dec. 31, 2017
Discontinued Operations and Disposal Groups [Abstract]
Held for Sale and Discontinued Operations	Held for Sale and Discontinued Operations Assets and liabilities of properties sold or classified as held for sale are separately identified on the Company’s Consolidated Balance Sheets in the current period. During 2017, the Company reclassified eight properties to held for sale. See "Potential Dispositions" in Note 4 for more information regarding seven of these properties. As of December 31, 2017 and 2016 , the Company had eight and two properties, respectively, classified as held for sale. During 2017, the Company sold the property remaining in assets held for sale that was classified as discontinued operations prior to the adoption of Accounting Standards Update No. 2014-08, “Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity”. None of the Company's 2016 or 2017 dispositions or assets classified as held for sale represented a strategic shift that had or will have a major effect on the Company's operations and financial results. Therefore, the 2016 and 2017 dispositions were not classified as discontinued operations. The table below reflects the assets and liabilities of the properties classified as held for sale and discontinued operations as of December 31, 2017 and 2016 . December 31, (Dollars in thousands) 2017 2016 Balance Sheet data Land $ 4,636 $ 1,362 Buildings, improvements and lease intangibles 63,654 4,410 Personal property 82 — 68,372 5,772 Accumulated depreciation (35,790 ) (2,977 ) Assets held for sale, net 32,582 2,795 Other assets, net (including receivables) 565 297 Assets of discontinued operations, net 565 297 Assets held for sale and discontinued operations, net $ 33,147 $ 3,092 Accounts payable and accrued liabilities $ 38 $ 22 Other liabilities 55 592 Liabilities of assets held for sale and discontinued operations $ 93 $ 614 The table below reflects the results of operations of the properties included in discontinued operations on the Company’s Consolidated Statements of Income for the years ended December 31, 2017 , 2016 and 2015 . Year Ended December 31, (Dollars in thousands, except per share data) 2017 2016 2015 Statements of Income data: Revenues (1) Rental income $ — $ — $ 752 Other operating — — — — — 752 Expenses (2) Property operating 19 71 58 Bad debt, net of recoveries (10 ) — (1 ) 9 71 57 Other Income (Expense) (3) Interest and other income, net — — 20 — — 20 Income (Loss) from Discontinued Operations (9 ) (71 ) 715 Impairments (4) — (121 ) (686 ) Gain on sales of real estate properties (5) 5 7 10,571 Income (Loss) from Discontinued Operations $ (4 ) $ (185 ) $ 10,600 Income (Loss) from Discontinued Operations per Common Share - Basic $ 0.00 $ 0.00 $ 0.11 Income (Loss) from Discontinued Operations per Common Share - Diluted $ 0.00 $ 0.00 $ 0.11 ______ (1) Total revenues for the year ended December 31, 2015 included $0.8 million related to properties sold. (2) Total expenses for the year ended December 31, 2016 included $0.1 million related to a property that is held for sale. Total expenses for the year ended December 31, 2015 included $0.1 million related to properties sold. (3) Other income (expense) for the year ended December 31, 2015 included income (expense) related to properties sold. (4) Impairments for the years ended December 31, 2016 and 2015 included $0.1 million and $0.7 million , respectively, related to one property sold. (5) Gain on sales of real estate properties for the year ended December 31, 2017 included a gain on the sale of one property sold in 2017. Gain on sales of real estate properties for the year ended December 31, 2016 included a gain on the sale of one property sold in 2015. Gains on the sales of real estate properties for the year ended December 31, 2015 included gains on the sale of one property.

Impairment Charges

Impairment Charges	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Impairment Charges	Impairment Charges An asset is impaired when undiscounted cash flows expected to be generated by the asset are less than the carrying value of the asset. The Company must assess the potential for impairment of its long-lived assets, including real estate properties, whenever events occur or there is a change in circumstances, such as the sale of a property or the decision to sell a property, that indicate that the recorded value might not be fully recoverable. The Company recorded impairment charges on properties sold or classified as held for sale, included in discontinued operations, for the years ended December 31, 2016 and 2015 totaling $0.1 million and $0.7 million , respectively. The Company recorded impairment charges on two properties sold in 2017 and two properties sold in 2015, included in continuing operations, for the years ended December 31, 2017 and 2015 totaling $5.4 million and $3.6 million , respectively. Both level 1 and level 3 fair value techniques were used to derive these impairment charges.

Other Assets

Other Assets	12 Months Ended
	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Other Assets	Other Assets Other assets consist primarily of straight-line rent receivables, prepaids, intangible assets, deferred financing costs and accounts receivable. Items included in "Other assets, net" on the Company’s Consolidated Balance Sheets as of December 31, 2017 and 2016 are detailed in the table below: December 31, (Dollars in millions) 2017 2016 Prepaid assets $ 65.2 $ 64.8 Equity investment in joint ventures 8.7 — Straight-line rent receivables 67.0 64.6 Above-market intangible assets, net 17.9 19.1 Additional long-lived assets, net 24.9 14.5 Ground lease modification, net 10.3 10.8 Accounts receivable 7.4 8.1 Allowance for uncollectible accounts (0.3 ) (0.1 ) Credit facility deferred financing costs 3.5 4.9 Goodwill 3.5 3.5 Customer relationship intangible assets, net 1.7 1.8 Other 3.2 3.7 $ 213.0 $ 195.7 Unconsolidated Joint Ventures During the fourth quarter of 2017, the Company purchased a non-managing membership interest in LLCs that own two parking garages in Atlanta, Georgia for $8.7 million which is included in the equity investment in joint ventures line in the table above. The parking garage interests were purchased in connection with three buildings that were acquired in the fourth quarter of 2017. The Company's investment in and income (loss) recognized for the year ended December 31, 2017 related to its LLCs accounted for under the equity method are shown in the table below: (Dollars in millions) December 31, 2017 Net LLC investment, beginning of period $ — New investments during the period 8.7 Equity income (loss) recognized during the period — Net LLC investments, end of period $ 8.7

Intangible Assets and Liabiliti

Intangible Assets and Liabilities	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets and Liabilities	Intangible Assets and Liabilities The Company has several types of intangible assets and liabilities included in its Consolidated Balance Sheets, including goodwill, deferred financing costs, above-, below-, and at-market lease intangibles, and customer relationship intangibles. The Company’s intangible assets and liabilities as of December 31, 2017 and 2016 consisted of the following: Gross Balance at December 31, Accumulated Amortization at December 31, Weighted Avg. Remaining Life (Years) Balance Sheet Classification (Dollars in millions) 2017 2016 2017 2016 Goodwill $ 3.5 $ 3.5 $ — $ — N/A Other assets Credit facility deferred financing costs 5.4 5.4 1.9 0.5 2.6 Other assets Above-market lease intangibles 22.9 24.5 5.0 5.4 57.8 Other assets Customer relationship intangibles 2.6 2.6 0.9 0.8 25.6 Other assets Below-market lease intangibles (9.5 ) (8.8 ) (3.5 ) (3.2 ) 36.5 Other liabilities Deferred financing costs 9.3 9.4 1.8 4.0 4.5 Notes and Bonds Payable At-market lease intangibles 110.0 84.1 41.6 39.0 5.6 Real estate properties $ 144.2 $ 120.7 $ 47.7 $ 46.5 15.2 The following table represents expected amortization over the next five years of the Company’s intangible assets and liabilities in place as of December 31, 2017 : (Dollars in millions) Future Amortization of Intangibles, net 2018 $ 19.8 2019 17.6 2020 12.0 2021 6.8 2022 5.8

Notes and Bonds Payable

Notes and Bonds Payable	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Notes and Bonds Payable	Notes and Bonds Payable December 31, Maturity Dates Contractual Interest Rates Principal Payments Interest Payments (Dollars in thousands) 2017 2016 Unsecured Credit Facility $ 189,000 $ 107,000 7/20 LIBOR + 1.00% At maturity Monthly Unsecured Term Loan due 2022 (1) 148,994 149,491 12/22 LIBOR + 1.10% At maturity Monthly Senior Notes due 2021 (1) — 397,147 1/21 5.75 % At maturity Semi-Annual Senior Notes due 2023 (1) 247,703 247,296 4/23 3.75 % At maturity Semi-Annual Senior Notes due 2025 (1) 248,044 247,819 5/25 3.88 % At maturity Semi-Annual Senior Notes due 2028 (1) 294,757 — 1/28 3.63 % At maturity Semi-Annual Mortgage notes payable (2) 155,382 115,617 12/18-5/40 3.31%-6.88% Monthly Monthly $ 1,283,880 $ 1,264,370 ______ (1) Balances are shown net of discounts and unamortized issuance costs. (2) Balances are shown net of discounts and unamortized issuance costs and including premiums. The Company’s various debt agreements contain certain representations, warranties, and financial and other covenants customary in such loan agreements. Among other things, these provisions require the Company to maintain certain financial ratios and impose certain limits on the Company’s ability to incur indebtedness and create liens or encumbrances. As of December 31, 2017 , the Company was in compliance with its financial covenant provisions under its various debt instruments. Unsecured Credit Facility due 2020 On October 14, 2011, the Company entered into a $700.0 million unsecured credit facility with a syndicate of lenders (the "Unsecured Credit Facility"). On July 29, 2016, the Company entered into the third amendment to the Unsecured Credit Facility to extend the maturity date to July 2020. The credit facility agreement provides the Company with two six -month extension options that could extend the maturity date to July 2021. Each option is subject to an extension fee of 0.075% of the aggregate commitments. Amounts outstanding under the Unsecured Credit Facility bear interest at LIBOR plus an applicable margin rate. The margin rate, which depends on the Company's credit ratings, ranges from 0.83% to 1.55% ( 1.00% as of December 31, 2017 ). In addition, the Company pays a facility fee per annum on the aggregate amount of commitments ranging from 0.13% to 0.30% ( 0.20% as of December 31, 2017 ). As of December 31, 2017 , the Company had $189.0 million outstanding under the Unsecured Credit Facility with an effective interest rate of approximately 2.56% and had a remaining borrowing capacity of approximately $511.0 million . Unsecured Term Loan due 2022 In February 2014, the Company entered into a $200.0 million unsecured term loan with a syndicate of nine lenders. On July 5, 2016, the Company repaid $50.0 million of the outstanding principal. On December 18, 2017, the Company entered into an amendment to the unsecured term loan due 2022 (the "Unsecured Term Loan due 2022") with a syndicate of nine lenders to extend the maturity date to December 2022. The Unsecured Term Loan due 2022 bears interest at a rate equal to (x) LIBOR plus (y) a margin ranging from 0.90% to 1.75% ( 1.10% as of December 31, 2017 ) based upon the Company's unsecured debt ratings. Payments under the Unsecured Term Loan due 2022 are interest only, with the full amount of the principal due at maturity. The Unsecured Term Loan due 2022 may be prepaid at any time, without penalty. The proceeds from the Unsecured Term Loan due 2022 were used by the Company to repay borrowings on the Unsecured Credit Facility. The Unsecured Term Loan due 2022 has various financial covenant provisions that are required to be met on a quarterly and annual basis that are equivalent to those of the Unsecured Credit Facility. On December 20, 2017, the Company entered into two interest rate swaps totaling $25.0 million to hedge the 1-month LIBOR portion of the cost of borrowing under the Unsecured Term Loan due 2022 to a fixed interest rate of 2.18% (plus the applicable margin rate) through December 2022. On January 30, 2018, the Company entered into two additional interest rate swaps totaling $50.0 million to hedge the 1-month LIBOR portion of the cost of borrowing under the Unsecured Term Loan due 2022 to a fixed interest rate of 2.46% (plus the applicable margin rate) through December 2022. The outstanding balance on the Unsecured Term Loan due 2022 was $150.0 million as of December 31, 2017 with an effective interest rate of approximately 2.77% including the impact of the interest rate swaps. Senior Notes due 2021 Redemption During the fourth quarter of 2017, the Company redeemed the outstanding principal of $400.0 million on its Senior Notes due 2021 in two transactions. On November 1, 2017 and December 27, 2017, the Company redeemed $100.0 million and $300.0 million , respectively. The aggregate redemption price of $452.3 million , consisting of outstanding principal of $400.0 million , accrued interest of $9.5 million , and a "make-whole" amount of approximately $42.8 million for the early extinguishment of debt. The unaccreted discount and unamortized costs on these notes of $2.2 million was written off upon redemption. The Company recognized a loss on early extinguishment of debt of approximately $45.0 million related to this redemption. The following table reconciles the balance of the Senior Notes due 2021 on the Company’s Consolidated Balance Sheets as of December 31, 2017 and 2016 : December 31, (Dollars in thousands) 2017 2016 Senior Notes due 2021 face value $ — $ 400,000 Unaccreted discount — (1,510 ) Issuance costs — (1,343 ) Senior Notes due 2021 carrying amount $ — $ 397,147 Senior Notes due 2023 On March 26, 2013, the Company issued $250.0 million of unsecured senior notes due 2023 (the "Senior Notes due 2023") in a registered public offering. The Senior Notes due 2023 bear interest at 3.75% , payable semi-annually on April 15 and October 15, beginning October 15, 2013, and are due on April 15, 2023, unless redeemed earlier by the Company. The notes were issued at a discount of approximately $2.1 million and the Company incurred debt issuance cost of $2.1 million , which yielded a 3.95% interest rate per annum upon issuance. For each of the years ended December 31, 2017 , 2016 and 2015 , the Company amortized approximately $0.2 million of the discount and $0.2 million of the debt issuance cost which are included in interest expense on the Company’s Consolidated Statements of Income. The following table reconciles the balance of the Senior Notes due 2023 on the Company’s Consolidated Balance Sheets as of December 31, 2017 and 2016 : December 31, (Dollars in thousands) 2017 2016 Senior Notes due 2023 face value $ 250,000 $ 250,000 Unaccreted discount (1,178 ) (1,375 ) Issuance costs (1,119 ) (1,329 ) Senior Notes due 2023 carrying amount $ 247,703 $ 247,296 Senior Notes due 2025 On April 24, 2015, the Company issued $250.0 million of unsecured senior notes due 2025 (the "Senior Notes due 2025") in a registered public offering. The Senior Notes due 2025 bear interest at 3.875% , payable semi-annually on May 1 and November 1, beginning November 1, 2015, and are due on May 1, 2025, unless redeemed earlier by the Company. The notes were issued at a discount of approximately $0.2 million and the Company incurred approximately $2.3 million in debt issuance costs which yielded a 4.08% interest rate per annum upon issuance. For the years ended December 31, 2017 , 2016 , and 2015 the Company amortized approximately $0.2 million , $ 0.2 million , and $ 0.1 million , respectively, of the debt issuance costs which is included in interest expense on the Company's Consolidated Statements of Income. Concurrent with this transaction, the Company settled four forward starting swap agreements for $1.7 million . The Senior Notes due 2025 have various financial covenants that are required to be met on a quarterly and annual basis. The following table reconciles the balance of the Senior Notes due 2025 on the Company’s Consolidated Balance Sheets as of December 31, 2017 and 2016 : December 31, (Dollars in thousands) 2017 2016 Senior Notes due 2025 face value $ 250,000 $ 250,000 Unaccreted discount (160 ) (178 ) Issuance costs (1,796 ) (2,003 ) Senior Notes due 2025 carrying amount $ 248,044 $ 247,819 Senior Notes due 2028 On December 11, 2017, the Company issued $300.0 million of unsecured Senior Notes due 2028 (the "Senior Notes due 2028") in a registered public offering. The Senior Notes due 2028 bear interest at 3.625% , payable semi-annually on January 15 and July 15, beginning July 15, 2018, and are due on January 15, 2028, unless redeemed earlier by the Company. The notes were issued at a discount of approximately $2.5 million and the Company incurred approximately $2.7 million in debt issuance costs which yielded a 3.84% interest rate per annum upon issuance. The Senior Notes due 2028 have various financial covenants that are required to be met on a quarterly and annual basis. The following table reconciles the balance of the Senior Notes due 2028 on the Company’s Consolidated Balance Sheets as of December 31, 2017 : (Dollars in thousands) December 31, 2017 Senior Notes due 2028 face value $ 300,000 Unaccreted discount (2,529 ) Issuance costs $ (2,714 ) Senior Notes due 2028 carrying amount $ 294,757 Mortgage Notes Payable The following table reconciles the Company’s aggregate mortgage notes principal balance with the Company’s Consolidated Balance Sheets as of December 31, 2017 and 2016 . For the years ended December 31, 2017 , 2016 and 2015 , the Company amortized approximately $0.3 million , $0.3 million and $0.8 million of the discount and $0.7 million , $0.9 million , and $1.0 million of the premium. For the years ended December 31, 2017, 2016 and 2015, the Company also amortized approximately $0.1 million , $0.2 million , and $0.2 million of the debt issuance costs, respectively, on the mortgage notes payable which is included in interest expense on the Company’s Consolidated Statements of Income. December 31, (Dollars in thousands) 2017 2016 Mortgage notes payable principal balance $ 154,916 $ 114,934 Unamortized premium 2,651 2,569 Unaccreted discount (1,332 ) (1,450 ) Issuance costs (853 ) (436 ) Mortgage notes payable carrying amount $ 155,382 $ 115,617 The following table details the Company’s mortgage notes payable, with related collateral. Original Balance Effective Interest Rate (23) Maturity Date Collateral (24) Principal and Interest Payments (22) Investment in Collateral at December 31, Balance at December 31, (Dollars in millions) 2017 2017 2016 Life Insurance Co. (1) 7.0 5.53 % 1/18 MOB Monthly/15-yr amort. $ — $ — $ 0.7 Commercial Bank (2) 1.8 5.55 % 10/30 OTH Monthly/27-yr amort. — — 1.3 Insurance Co. (3) 7.3 5.54 % 12/18 MOB Monthly/25-yr amort. 14.3 6.0 6.2 Commercial Bank (4) 9.5 5.07 % 3/19 MOB Monthly/5-yr amort. 13.9 9.3 9.5 Commercial Bank (5) 9.4 4.55 % 7/19 MOB Monthly/8-yr amort 27.8 9.2 9.3 Commercial Bank (6) 15.2 7.65 % 7/20 MOB (21) 20.2 12.7 12.7 Life Insurance Co. (7) 7.9 4.00 % 8/20 MOB Monthly/15-yr amort. 20.7 2.0 2.7 Life Insurance Co. (8) 7.3 5.25 % 8/20 MOB Monthly/27-yr amort. 17.9 6.5 6.7 Life Insurance Co. (9) 5.6 4.27 % 1/21 MOB Monthly/10-yr amort. 15.7 4.8 — Commercial Bank (10) 12.9 6.43 % 2/21 MOB Monthly/12-yr amort. 54.9 10.5 10.7 Life Insurance Co. (11) 11.0 3.85 % 11/22 MOB Monthly/7-yr amort. 22.0 10.4 — Life Insurance Co. (12) 12.3 3.85 % 8/23 MOB Monthly/7-yr amort. 24.6 11.5 — Financial Services (13) 12.4 4.27 % 10/23 MOB Monthly/10-yr amort. 24.7 12.2 — Life Insurance Co. (14) 13.3 4.13 % 1/24 MOB Monthly/10-yr amort. 21.1 13.3 13.6 Life Insurance Co. (15) 6.8 3.94 % 2/24 MOB Monthly/7-yr amort. 14.5 6.7 — Financial Services (16) 9.7 4.32 % 9/24 MOB Monthly/10-yr amort. 16.4 8.8 9.1 Commercial Bank 11.5 3.71 % 1/26 MOB Monthly/10-yr amort. 37.9 10.5 11.0 Commercial Bank (17) 15.0 5.25 % 4/27 MOB Monthly/20-yr amort. 33.4 9.6 10.4 Municipal Government (18) (19) 11.0 4.79 % (20) MOB Semi-Annual (20) 20.9 11.4 11.7 $ 400.9 $ 155.4 $ 115.6 ______ (1) The Company repaid this mortgage note in October 2017. The Company's unencumbered gross investment was $14.3 million at December 31, 2017. (2) The Company repaid this mortgage note in September 2017. The Company's unencumbered gross investment was $8.0 million at December 31, 2017. (3) The unamortized portion of the $0.6 million premium recorded on this note upon acquisition is included in the balance above. (4) The unamortized portion of the $0.2 million premium recorded on this note upon acquisition is included in the balance above. (5) The unamortized portion of the $0.3 million premium recorded on this note upon acquisition is included in the balance above. (6) The unaccreted portion of the $2.4 million discount recorded on this note upon acquisition is included in the balance above. (7) The unamortized portion of the $0.3 million premium recorded on this note upon acquisition is included in the balance above. (8) The unamortized portion of the $0.4 million premium recorded on this note upon acquisition is included in the balance above. (9) The unamortized portion of the $0.2 million premium recorded on this note upon acquisition is included in the balance above. (10) The unaccreted portion of the $1.0 million discount recorded on this note upon acquisition is included in the balance above. (11) The unaccreted portion of the $0.1 million discount recorded on this note upon acquisition is included in the balance above. (12) The unaccreted portion of the $0.2 million discount recorded on this note upon acquisition is included in the balance above. (13) The unamortized portion of the $0.4 million premium recorded upon acquisition is included in the balance above. (14) The unamortized portion of the $0.8 million premium recorded on this note upon acquisition is included in the balance above. (15) The unamortized portion of the $0.2 million premium recorded on this note upon acquisition is included in the balance above. (16) The unamortized portion of the $0.1 million premium recorded on this note upon acquisition is included in the balance above. (17) The unamortized portion of the $0.7 million premium recorded on this note upon acquisition is included in the balance above. (18) Balance consists of three notes secured by the same building. (19) The unamortized portion of the $1.0 million premium recorded on the three notes upon acquisition is included in the balance above. (20) These three mortgage notes payable are series municipal bonds that have maturity dates ranging from from May 2022 to May 2040. One of the four original notes payable was repaid upon maturity in May 2017. The remaining three require interest only payments and have future maturity dates but allow repayment after May 2020 without penalty. The Company intends on repaying all three notes payable at that time. (21) Payable in monthly installments of interest only for 24 months and then installments of principal and interest based on an 11 -year amortization with the final payment due at maturity. (22) Payable in monthly installments of principal and interest with the final payment due at maturity (unless otherwise noted). (23) The contractual interest rates for the 19 outstanding mortgage notes ranged from 3.3% to 6.9% as of December 31, 2017 . (24) MOB-Medical office building; OTH-Other. Other Long-Term Debt Information Future maturities of the Company’s notes and bonds payable as of December 31, 2017 were as follows: (Dollars in thousands) Principal Maturities Net Accretion/ Amortization (1) Debt Issuance Costs (2) Notes and Bonds Payable % 2018 $ 10,605 $ (18 ) $ (1,051 ) 9,536 0.7 % 2019 22,711 (224 ) (1,044 ) 21,443 1.7 % 2020 211,803 (382 ) (1,039 ) 210,382 16.4 % 2021 17,321 (312 ) (1,025 ) 15,984 1.2 % 2022 162,692 (328 ) (1,037 ) 161,327 12.6 % 2023 and thereafter 868,784 (1,284 ) (2,292 ) 865,208 67.4 % $ 1,293,916 $ (2,548 ) $ (7,488 ) 1,283,880 100.0 % ______ (1) Includes discount accretion and premium amortization related to the Company’s Senior Notes due 2023, Senior Notes due 2025, Senior Notes due 2028 and 18 mortgage notes payable. (2) Excludes approximately $3.5 million in debt issuance costs related to the Company's Unsecured Credit Facility due 2020 included in other assets.

Derivative Financial Instrument

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Derivative Financial Instruments Risk Management Objective of Using Derivatives The Company is exposed to certain risk arising from both its business operations and economic conditions. The Company principally manages its exposures to a wide variety of business and operational risks through management of its core business activities. The Company manages economic risks, including interest rate, liquidity, and credit risk, primarily by managing the amount, sources, and duration of its assets and liabilities and the use of derivative financial instruments. Specifically, the Company enters into derivative financial instruments to manage exposures that arise from business activities that result in the receipt or payment of future known and uncertain cash amounts, the value of which are determined by interest rates. The Company’s derivative financial instruments are used to manage differences in the amount, timing, and duration of the Company’s known or expected cash receipts and its known or expected cash payments principally related to the Company’s borrowings. Cash Flow Hedges of Interest Rate Risk The Company’s objectives in using interest rate derivatives are to add stability to interest expense and to manage its exposure to interest rate movements. To accomplish this objective, the Company primarily uses interest rate swaps as part of its interest rate risk management strategy. Interest rate swaps designated as cash flow hedges involve the receipt of variable amounts from a counterparty in exchange for the Company making fixed-rate payments over the life of the agreements without exchange of the underlying notional amount. During 2017, such derivatives were used to hedge the variable cash flows associated with existing variable-rate debt. 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 (Loss) and subsequently reclassified into interest expense in the same period(s) during which the hedged transaction affects earnings. Amounts reported in accumulated other comprehensive income related to derivatives will be reclassified to interest expense as interest payments are made on the Company’s variable-rate debt. During the year ended December 31, 2017 , the Company entered into two outstanding interest rate derivatives that were designated as cash flow hedges of interest rate risk: Interest Rate Derivative Number of Instruments Notional (in millions) Interest rate swaps 2 $25.0 During the year ended December 31, 2015, the Company entered into four forward starting interest rate swaps with a total notional value of $225.0 million to hedge the risk of changes in the interest-related cash flows associated with the potential issuance of long-term debt. That debt was issued in April 2015, as discussed in Note 9, and the forward starting interest rate swaps were terminated. As a result, the Company realized a loss at the termination date which was deferred and is being amortized over the term of the Senior Notes due 2025. Tabular Disclosure of Fair Values of Derivative Instruments on the Balance Sheet The table below presents the fair value of the Company's derivative financial instruments, as well as, their classification on the Consolidated Balance Sheets as of December 31, 2017. Liability Derivatives As of December 31, 2017 (Dollars in thousands) Balance Sheet Location Fair Value Derivatives designated as hedging instruments Interest rate swaps Other liabilities $ 67 Total derivatives designated as hedging instruments $ 67 Tabular Disclosure of the Effect of Fair Value and Cash Flow Hedge Accounting on Accumulated Other Comprehensive Income (Loss) The table below presents the effect of cash flow hedge accounting on Accumulated Other Comprehensive Income (Loss) as of December 31, 2017 related to the Company's outstanding interest rate swaps. Amount of Loss Recognized in OCI on Derivative Amount of Loss Reclassified from OCI into Income (Dollars in thousands) 2017 2017 2016 Interest rate products $ 74 Interest expense $ 7 $ — Settled interest rate swaps — Interest expense 169 168 $ 74 Total interest expense $ 176 $ 168 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 December 31, 2017, the fair value of derivatives in a net liability position, which includes accrued interest but excludes any adjustment for nonperformance risk, related to these agreements was $0.1 million . If the Company had breached any of these provisions at December 31, 2017, it could have been required to settle its obligations under the agreements at their termination value of $0.1 million . The Company estimates that an additional $0.3 million will be reclassified from accumulated other comprehensive loss as an increase to interest expense over the next 12 months. Subsequent Activity On January 30, 2018, the Company entered into two interest rate derivatives that were designated as cash flow hedges of interest rate risk totaling $50.0 million . These derivatives were used to hedge variable cash flows associated with variable-rate debt.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Common Stock The Company had no preferred shares outstanding and had common shares outstanding for the three years ended December 31, 2017 as follows: Year Ended December 31, 2017 2016 2015 Balance, beginning of year 116,416,900 101,517,009 98,828,098 Issuance of common stock 8,395,607 14,063,100 2,493,171 Non-vested stock-based awards, net of withheld shares and forfeitures 319,086 836,791 195,740 Balance, end of year 125,131,593 116,416,900 101,517,009 Equity Offering On August 14, 2017, the Company issued 8,337,500 shares of common stock par value $0.01 per share, at $30.90 per share in an underwritten public offering pursuant to the Company's existing effective registration statement. The net proceeds of the offering, after underwriting discount and offering expenses, were approximately $247.1 million . At-The-Market Equity Offering Program The Company has in place an at-the-market equity offering program to sell shares of the Company’s common stock from time to time in at-the-market sales transactions. The following table details the shares sold under this program. Shares Sold Sales Price Per Share Net Proceeds (in millions) 2017 — NA $ — 2016 4,795,601 $28.31 - $33.66 $ 144.6 2015 2,434,239 $25.00 - $29.15 $ 65.8 On February 19, 2016, the Company entered into sales agreements with five investment banks to allow sales under its at-the-market equity offering program of up to 10,000,000 shares of common stock. A previous sales agreement with one investment bank was terminated effective February 17, 2016. No shares were sold related to this program during 2017. On May 5, 2017, the Company entered into a sales agreement with a sixth investment bank in connection with the same allotment of shares. The Company has 5,868,697 authorized shares remaining available to be sold under the current sales agreements as of February 14, 2018 . Dividends Declared During 2017 , the Company declared and paid common stock dividends aggregating $1.20 per share ( $0.30 per share per quarter). On February 13, 2018, the Company declared a quarterly common stock dividend in the amount of $0.30 per share payable on March 6, 2018 to stockholders of record on February 23, 2018. Common Stock Authorization On May 2, 2017, the Company's shareholders approved an amendment to the Company's Articles of Incorporation to increase the number of authorized shares of common stock from 150,000,000 to 300,000,000 . Authorization to Repurchase Common Stock The Company’s Board of Directors has authorized management to repurchase up to 3,000,000 shares of the Company’s common stock. As of December 31, 2017 , the Company had not repurchased any shares under this authorization. The Company may elect, from time to time, to repurchase shares either when market conditions are appropriate or as a means to reinvest excess cash flows. Such purchases, if any, may be made either in the open market or through privately negotiated transactions. Accumulated Other Comprehensive Income (Loss) During the year ended December 31, 2017, the Company entered into two interest rate swaps to hedge the variable cash flows associated with existing variable-rate debt. The Company recorded a loss in accumulated other comprehensive loss of approximately $0.1 million as of December 31, 2017. The Company continues to amortize the 2015 settlement of forward-starting interest rate swaps. This amount will be reclassified out of accumulated other comprehensive loss impacting net income over the 10 -year term of the associated senior note issuance. See Note 10 for more information regarding the Company's derivative instruments. The following table represents the changes in accumulated other comprehensive loss during the year ended December 31, 2017 : (Dollars in thousands) Interest Rate Swaps Beginning balance $ (1,401 ) Other comprehensive loss before reclassifications 176 Amounts reclassified from accumulated other comprehensive income (loss) (74 ) Net current-period other comprehensive income 102 Ending balance $ (1,299 ) The following table represents the details regarding the reclassifications from Accumulated other comprehensive income (loss) during the year ended December 31, 2017 : Details about accumulated other comprehensive income (loss) components Amount reclassified from accumulated other comprehensive income (loss) Affected line item in the statement where net income is presented (Dollars in thousands) Amounts reclassified from accumulated other comprehensive income (loss) related to settled interest rate swaps $ 169 Interest Expense Amounts reclassified from accumulated other comprehensive income (loss) related to current interest rate swaps 7 Interest Expense $ 176

Benefit Plans

Benefit Plans	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Benefit Plans	Benefit Plans Executive Retirement Plan Effective May 5, 2015, the Company terminated its Executive Retirement Plan and recorded a charge of approximately $5.3 million , inclusive of the acceleration of $2.5 million recorded in accumulated other comprehensive loss on the Company's Consolidated Balance Sheet that was being amortized resulting in a total benefit obligation of $19.6 million in connection with the termination of the Executive Retirement Plan. The charge includes amounts resulting from assumed additional years of service for two plan participants who had not reached age 65 and payments associated with FICA and other tax obligations. On May 6, 2016, the Company paid the total benefit obligation of $19.6 million which reduced Other liabilities on the Company's Consolidated Balance Sheets. As a result of the termination of the plan, and included in the payment of the total benefit obligation, Mr. Emery received a lump sum amount equal to his accrued benefit under the plan of approximately $14.4 million in May 2016. Net periodic benefit cost for the Executive Retirement Plan for the three years in the period ended December 31, 2017 is comprised of the following: Year Ended December 31, (Dollars in thousands) 2017 2016 2015 Service cost $ — $ — $ 29 Interest cost — — 225 Amortization of prior service cost (benefit) — — (198 ) Amortization of net gain — — 343 — — 399 Net loss recognized in Accumulated other comprehensive income (loss) — — — Total recognized in net periodic benefit gain and Accumulated other comprehensive income (1) $ — $ — $ 399 _____ (1) 2015 is a partial year due to the termination of the Executive Retirement Plan during the year. The Company had no benefit obligations as of December 31, 2017 and 2016 .

Stock and Other Incentive Plans

Stock and Other Incentive Plans	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock and Other Incentive Plans	Stock and Other Incentive Plans Stock Incentive Plan In May 2015, the Company's stockholders approved the 2015 Stock Incentive Plan (the "2015 Incentive Plan") which authorizes the Company to issue 3,500,000 shares of common stock to its employees and directors. The 2015 Incentive Plan, which superseded the 2007 Employee Stock Incentive Plan (the "Predecessor Plan"), will continue until terminated by the Company’s Board of Directors. As of December 31, 2017 and 2016 , the Company had issued a total of 1,438,228 and 1,024,739 restricted shares, respectively, under the 2015 Incentive Plan for compensation-related awards to employees and directors, with a total of 2,061,772 and 2,475,261 , respectively, remaining which had not been issued. Under the Predecessor Plan for compensation-related awards to employees and directors, the Company had issued, net of forfeitures, a total of 1,878,637 restricted shares for the year ended December 31, 2015. Non-vested shares issued under the 2015 Incentive Plan are generally subject to fixed vesting periods varying from three to eight years beginning on the date of issue. If a recipient voluntarily terminates his or her relationship with the Company or is terminated for cause before the end of the vesting period, the shares are forfeited, at no cost to the Company. The Company recognizes the impact of forfeitures as they occur. Once the shares have been issued, the recipient has the right to receive dividends and the right to vote the shares. Compensation expense recognized during the years ended December 31, 2017 , 2016 and 2015 from the amortization of the value of shares over the vesting period issued to employees and directors was $9.8 million , $7.4 million and $5.9 million , respectively. The following table represents expected amortization of the Company's non-vested shares issued: (Dollars in millions) Future Amortization of Non-Vested Shares 2018 $ 9.4 2019 7.0 2020 6.7 2021 5.7 2022 3.2 2023 and thereafter 3.6 Total $ 35.6 Executive Incentive Plan On July 31, 2012, the Company adopted an Executive Incentive Plan, which was amended and restated on February 16, 2016 ("Executive Incentive Plan"), to provide specific award criteria with respect to incentive awards made under the 2015 Incentive Plan subject to the discretion of the Compensation Committee. No new shares of common stock were authorized in connection with the Executive Incentive Plan. Under the terms of the Executive Incentive Plan, the Company's named executive officers, and certain other members of senior management, may earn incentive awards in the form of cash and non-vested stock. Cash incentive awards are based on individual and Company performance. Company performance is measured over a four-quarter period against targeted financial and operational metrics set in advance by the Compensation Committee. Non-vested stock awards are based on the Company's relative total shareholder return ("TSR") performance over one -year and three -year periods, measured against the Company's peer group. For 2017 , 2016 and 2015 , compensation expense resulting from the amortization of non-vested share grants to officers was approximately $5.0 million , $4.0 million , and $2.7 million , respectively. Details of the awards that have been earned from this plan are as follows: • On December 11, 2017, the Company granted non-vested stock awards for TSR performance to its five named executive officers and four senior vice presidents with a grant date fair value totaling $10.1 million , which were granted in the form of 309,874 non-vested shares, with a five -year vesting period, which will result in annual compensation expense of $2.0 million for the each of 2018, 2019, 2020, and 2021, and $1.9 million for 2022, respectively. • On December 16, 2016, the Company granted non-vested stock awards for TSR performance to its five named executive officers and five senior vice presidents with a grant date fair value totaling $6.3 million , which were granted in the form of 213,639 non-vested shares, with a five -year vesting period, which will result in annual compensation expense of $1.3 million each of 2018, 2019, and 2020, and $1.2 million for 2021, respectively. • On February 16, 2016, the Company granted cash incentive and non-vested performance-based awards totaling $5.8 million to its five named executive officers and five senior vice presidents. The officers could elect cash based awards or non-vested stock awards. Cash awards totaled $1.1 million . The non-vested awards, which the officers elected to receive in lieu of cash, had a grant date fair value totaling $4.7 million , which were granted in the form of 163,788 non-vested shares, with either a three - or five -year vesting period, resulting in annual compensation expense of $1.1 million for the year 2018 and $0.7 million for each of 2019 and 2020, respectively. • On December 18, 2015, the Company granted non-vested stock awards for TSR performance to its five named executive officers and five senior vice presidents with a grant date fair value totaling $3.9 million . The awards were granted in the form of 139,000 non-vested shares, with a three -year vesting period, which will result in annual compensation expense of $1.3 million for 2018. Long-Term Incentive Program In the first quarter of 2017 and 2016 , the Company granted a performance-based award to officers, excluding the five named executive officers and four senior vice presidents, under the Long-term Incentive Program adopted under the 2015 Incentive Plan (the "LTIP") totaling approximately $1.3 million per award, which was granted in the form of 41,368 non-vested shares and 44,162 non-vested shares, respectively. The shares have vesting periods ranging from three to eight years with a weighted average vesting period of approximately six years. Beginning in 2012, the Company's executive officers were no longer eligible to participate in the LTIP and beginning in 2013, five senior vice presidents were also no longer eligible to participate. For 2017 , 2016 and 2015 , compensation expense resulting from the amortization of non-vested share grants to officers was approximately $1.1 million . Salary Deferral Plan The Company's salary deferral plan allows certain of its officers to elect to defer up to 50% of their base salary in the form of non-vested shares issued under the 2015 Incentive Plan subject to long-term vesting. The number of shares will be increased through a Company match depending on the length of the vesting period selected by the officer. The officer's vesting period choices are: three years for a 30% match; five years for a 50% match; and eight years for a 100% match. During 2017 , 2016 and 2015 , the Company issued 39,016 shares, 42,256 shares and 55,923 shares, respectively, to its officers through the salary deferral plan. For 2017 , 2016 and 2015 , compensation expense resulting from the amortization of non-vested share grants to officers was approximately $1.2 million , $1.2 million , and $1.1 million , respectively. Non-employee Directors Incentive Plan The Company issues non-vested shares to its non-employee directors under the 2015 Incentive Plan. The directors’ shares issued have a one -year vesting period beginning with the May 2015 grant (previously a three -year vesting period) and are subject to forfeiture prior to such date upon termination of the director’s service, at no cost to the Company. During 2017 , 2016 and 2015 , the Company issued 23,231 shares, 21,374 shares, and 23,201 shares, respectively, to its non-employee directors through the 2015 Incentive Plan. For 2017 , 2016 and 2015 , compensation expense resulting from the amortization of non-vested share grants to directors was approximately $0.8 million , $1.0 million , and $1.0 million , respectively. Other Grants The Company issued three one-time non-vested share grants related to executive management transition in 2016. For 2017 and 2016 , compensation expense resulting from the amortization of these non-vested share grants to officers was approximately $1.7 million and $0.1 million , respectively. The following information provides information about each grant: • On March 1, 2016, the Company issued 50,000 shares to the Chief Financial Officer with a 10 -year vesting period, resulting in compensation expense of $0.2 million per year. • On December 30, 2016, the Company issued 200,000 shares to the President and Chief Executive Officer with a 10 -year vesting period, resulting in compensation expense of $0.6 million per year. • On December 30, 2016, the Company issued 150,000 shares to the Executive Chairman with a 5 -year vesting period, resulting in compensation expense of $0.9 million per year. A summary of the activity under the 2015 Incentive Plan and related information for the three years in the period ended December 31, 2017 follows: Year Ended December 31, (Dollars in thousands, except per share data) 2017 2016 2015 Stock-based awards, beginning of year 1,786,497 1,092,262 1,057,732 Granted 413,489 885,219 251,789 Vested (292,341 ) (190,984 ) (210,955 ) Forfeited — — (6,304 ) Stock-based awards, end of year 1,907,645 1,786,497 1,092,262 Weighted-average grant date fair value of: Stock-based awards, beginning of year $ 27.18 $ 24.72 $ 24.01 Stock-based awards granted during the year $ 32.05 $ 29.60 $ 27.70 Stock-based awards vested during the year $ 25.88 $ 24.34 $ 25.05 Stock-based awards forfeited during the year $ — $ — $ 24.80 Stock-based awards, end of year $ 28.44 $ 27.18 $ 24.72 Grant date fair value of shares granted during the year $ 13,254 $ 26,204 $ 6,975 The vesting periods for the non-vested shares granted during 2017 ranged from one to eight years with a weighted-average amortization period remaining as of December 31, 2017 of approximately 5.1 years. During 2017 , 2016 and 2015 , the Company withheld 94,403 shares, 48,248 shares and 49,225 shares, respectively, of common stock from its officers to pay estimated withholding taxes related to the vesting of shares. 401(k) Plan The Company maintains a 401(k) plan that allows eligible employees to defer salary, subject to certain limitations imposed by the Internal Revenue Code. The Company provides a matching contribution of up to 3% of each eligible employee’s salary, subject to certain limitations. The Company’s matching contributions were approximately $0.4 million for each year during 2017 , 2016 and 2015 . Dividend Reinvestment Plan The Company is authorized to issue 1,000,000 shares of common stock to stockholders under the Dividend Reinvestment Plan. As of December 31, 2017 , the Company had issued 581,627 shares under the plan of which 26,031 shares were issued in 2017 , 9,575 shares were issued in 2016 and 13,950 shares were issued in 2015 . Employee Stock Purchase Plan The Company has an Employee Stock Purchase Plan, pursuant to which the Company is authorized to issue shares of common stock. As of December 31, 2017 , 2016 and 2015 , the Company had a total of 25,535 shares, 63,690 shares and 96,977 shares authorized under the Employee Stock Purchase Plan, respectively, which had not been issued or optioned. Under the Employee Stock Purchase Plan, each eligible employee in January of each year is able to purchase up to $25,000 of common stock at the lesser of 85% of the market price on the date of grant or 85% of the market price on the date of exercise of such option. The number of shares subject to each year’s option becomes fixed on the date of grant. Options granted under the Employee Stock Purchase Plan expire if not exercised 27 months after each such option’s date of grant. Cash received from employees upon exercising options under the Employee Stock Purchase Plan was approximately $0.8 million for the year ended December 31, 2017 , $1.2 million for the year ended December 31, 2016 , and $0.9 million for the year ended December 31, 2015 . A summary of the Employee Stock Purchase Plan activity and related information for the three years in the period ended December 31, 2017 is as follows: Year Ended December 31, (Dollars in thousands, except per share data) 2017 2016 2015 Options outstanding, beginning of year 316,321 340,958 393,902 Granted 206,824 198,450 197,640 Exercised (32,076 ) (57,924 ) (44,462 ) Forfeited (40,659 ) (22,081 ) (47,176 ) Expired (132,310 ) (143,082 ) (158,946 ) Options outstanding and exercisable, end of year 318,100 316,321 340,958 Weighted-average exercise price of: Options outstanding, beginning of year $ 23.69 $ 20.70 $ 19.17 Options granted during the year $ 25.77 $ 24.07 $ 23.22 Options exercised during the year $ 24.31 $ 21.40 $ 19.41 Options forfeited during the year $ 25.01 $ 23.16 $ 19.90 Options expired during the year $ 23.22 $ 18.11 $ 20.41 Options outstanding, end of year $ 25.00 $ 23.69 $ 20.70 Weighted-average fair value of options granted during the year (calculated as of the grant date) $ 6.31 $ 5.37 $ 5.39 Intrinsic value of options exercised during the year $ 271 $ 634 $ 381 Intrinsic value of options outstanding and exercisable (calculated as of December 31) $ 2,683 $ 2,098 $ 2,597 Exercise prices of options outstanding (calculated as of December 31) $ 25.00 $ 23.69 $ 20.70 Weighted-average contractual life of outstanding options (calculated as of December 31, in years) 0.8 0.8 0.8 The fair values for these options were estimated at the date of grant using a Black-Scholes options pricing model with the weighted-average assumptions for the options granted during the period noted in the following table. The risk-free interest rate was based on the U.S. Treasury constant maturity-nominal two-year rate whose maturity is nearest to the date of the expiration of the latest option outstanding and exercisable; the expected dividend yield was based on the expected dividends of the current year as a percentage of the average stock price of the prior year; the expected life of each option was estimated using the historical exercise behavior of employees; expected volatility was based on historical volatility of the Company’s common stock; and expected forfeitures were based on historical forfeiture rates within the look-back period. 2017 2016 2015 Risk-free interest rates 1.20 % 1.06 % 0.67 % Expected dividend yields 3.70 % 4.64 % 4.79 % Expected life (in years) 1.45 1.42 1.38 Expected volatility 20.4 % 17.6 % 21.0 % Expected forfeiture rates 85 % 85 % 80 %

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share The Company uses the two-class method of computing net earnings per common shares. Non-vested share-based awards containing non-forfeitable rights to dividends are considered participating securities pursuant to the two-class method. The table below sets forth the computation of basic and diluted earnings per common share for the three years in the period ended December 31, 2017 . Year Ended December 31, (Dollars in thousands, except per share data) 2017 2016 2015 Weighted Average Common Shares Weighted average Common Shares outstanding 119,739,216 109,861,580 100,280,059 Non-vested shares (1,813,058 ) (1,289,478 ) (1,108,707 ) Weighted average Common Shares - Basic 117,926,158 108,572,102 99,171,352 Weighted average Common Shares - Basic 117,926,158 108,572,102 99,171,352 Dilutive effect of non-vested shares — 709,559 623,212 Dilutive effect of employee stock purchase plan 91,007 105,336 85,738 Weighted average Common Shares - Diluted 118,017,165 109,386,997 99,880,302 Net Income Income from continuing operations $ 23,096 $ 85,756 $ 58,836 Dividends paid on nonvested share-based awards (2,149 ) — — Income from continuing operations applicable to common stockholders 20,947 85,756 58,836 Discontinued operations (4 ) (185 ) 10,600 Net income applicable to common stockholders $ 20,943 $ 85,571 $ 69,436 Basic Earnings Per Common Share Income from continuing operations $ 0.18 $ 0.79 $ 0.59 Income from discontinued operations 0.00 0.00 0.11 Net income $ 0.18 $ 0.79 $ 0.70 Diluted Earnings Per Common Share Income from continuing operations $ 0.18 $ 0.78 $ 0.59 Income from discontinued operations 0.00 0.00 0.11 Net income $ 0.18 $ 0.78 $ 0.70

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Redevelopment Activity The Company completed the redevelopment and expansion of one medical office building in Nashville, Tennessee in 2017. The Company spent approximately $12.6 million on the redevelopment of this property during the year ended December 31, 2017 , including approximately $3.2 million related to overages on tenant improvement projects that have been or will be reimbursed by the tenant. During 2017, the Company began the redevelopment of a medical office building in Charlotte, North Carolina, which includes a 38,000 square foot vertical expansion. The Company spent approximately $3.3 million on the redevelopment during the year ended December 31, 2017. Development Activity The Company completed the development of a 99,957 square foot medical office building in Denver, Colorado. The Company spent approximately $14.6 million during the year ended December 31, 2017 , including approximately $2.8 million related to overages on tenant improvement projects that have been or will be reimbursed by the tenant. The Company anticipates funding additional tenant improvements throughout 2018 and 2019. The Company began the development of a 151,000 square foot medical office building in Seattle, Washington during 2017. The Company spent approximately $1.8 million on the development during the year ended December 31, 2017. The Company expects the project to be completed in the second quarter of 2019. The table below details the Company’s construction activity as of December 31, 2017 . The information included in the table below represents management’s estimates and expectations at December 31, 2017 , which are subject to change. The Company’s disclosures regarding certain projections or estimates of completion dates may not reflect actual results. December 31, 2017 (Dollars in thousands) Number of Properties Estimated Completion Date Construction in Progress Balance Total Funded During the Year Total Amount Funded Estimated Remaining Fundings (unaudited) Estimated Total Investment (unaudited) Approximate Square Feet (unaudited) Construction Activity Charlotte, NC 1 Q1 2019 $ 3,487 $ 3,264 $ 3,487 8,513 $ 12,000 204,000 Seattle, WA 1 Q2 2019 1,971 1,809 2,272 61,848 64,120 151,000 Total $ 5,458 $ 5,073 $ 5,759 $ 70,361 $ 76,120 355,000 Tenant Improvements The Company may provide a tenant improvement allowance in new or renewal leases for the purpose of refurbishing or renovating tenant space. As of December 31, 2017 , the Company had commitments of approximately $27.8 million that is expected to be spent on tenant improvements throughout the portfolio, excluding development properties currently under construction. Land Held for Development Land held for development includes parcels of land owned by the Company, upon which the Company intends to develop and own outpatient healthcare facilities. The Company’s investment in six parcels of land held for development located adjacent to certain of the Company's existing medical office buildings in Texas, Iowa and Tennessee totaled approximately $20.1 million as of December 31, 2017 and 2016 . Operating Leases As of December 31, 2017 , the Company was obligated under operating lease agreements consisting primarily of the Company’s corporate office lease and ground leases. At December 31, 2017 , the Company had 109 properties totaling 8.9 million square feet that were held under ground leases with a remaining weighted average term of 68.7 years, including renewal options. These ground leases typically have initial terms of 50 to 75 years with one to two renewal options extending the terms to 75 to 100 years, with expiration dates through 2117 . The Company’s ground leases generally increase annually based on increases in the Consumer Price Index. Rental expense relating to the operating leases for the years ended December 31, 2017 , 2016 and 2015 was $6.3 million , $5.7 million and $5.1 million , respectively. The Company prepaid 48 ground leases, which represented approximately $0.5 million of the Company’s rental expense for the years ended December 31, 2017 , 2016 , and 2015 . The Company’s corporate office lease currently covers approximately 36,653 square feet of rented space and expires on October 31, 2020. The Company’s future minimum lease payments for its corporate office lease and 61 ground leases, excluding leases that the Company has prepaid and leases in which an operator pays or fully reimburses the Company, as of December 31, 2017 were as follows (in thousands): 2018 $ 5,341 2019 5,420 2020 5,459 2021 5,488 2022 5,516 2023 and thereafter 283,056 $ 310,280

Other Data

Other Data	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Other Data	Other Data Taxable Income (unaudited) The Company has elected to be taxed as a REIT, as defined under the Internal Revenue Code. To qualify as a REIT, the Company must meet a number of organizational and operational requirements, including a requirement that it currently distribute at least 90% of its taxable income to its stockholders. As a REIT, the Company generally will not be subject to federal income tax on taxable income it distributes currently to its stockholders. Accordingly, no provision for federal income taxes has been made in the accompanying Consolidated Financial Statements. If the Company fails to qualify as a REIT for any taxable year, then it will be subject to federal income taxes at regular corporate rates, including any applicable alternative minimum tax, and may not be able to qualify as a REIT for four subsequent taxable years. Even if the Company qualifies as a REIT, it may be subject to certain state and local taxes on its income and property and to federal income and excise tax on its undistributed taxable income. Earnings and profits (as defined under the Internal Revenue Code), the current and accumulated amounts of which determine the taxability of distributions to stockholders, vary from net income attributable to common stockholders and taxable income because of different depreciation recovery periods, depreciation methods, and other items. On a tax-basis, the Company’s gross real estate assets totaled approximately $4.0 billion , $3.7 billion , and $3.4 billion as of December 31, 2017 , 2016 and 2015, respectively. The following table reconciles the Company’s consolidated net income attributable to common stockholders to taxable income for the three years ended December 31, 2017 : Year Ended December 31, (Dollars in thousands) 2017 2016 2015 Net income $ 23,092 $ 85,571 $ 69,436 Reconciling items to taxable income: Depreciation and amortization 46,426 38,260 30,457 Gain or loss on disposition of depreciable assets 1,570 (32,103 ) 1,659 Impairments — 121 687 Straight-line rent (4,551 ) (7,101 ) (8,833 ) Receivable allowances 1,680 2,067 571 Stock-based compensation 1,855 1,301 7,518 Other 6,552 2,236 4,304 53,532 4,781 36,363 Taxable income (1) $ 76,624 $ 90,352 $ 105,799 Dividends paid $ 142,327 $ 131,759 $ 120,266 ______ (1) Before REIT dividend paid deduction. Characterization of Distributions (unaudited) Distributions in excess of earnings and profits generally constitute a return of capital. The following table gives the characterization of the distributions on the Company’s common stock for the three years ended December 31, 2017 . For the three years ended December 31, 2017 , there were no preferred shares outstanding. As such, no dividends were distributed related to preferred shares for those periods. 2017 2016 2015 Per Share % Per Share % Per Share % Common stock: Ordinary income $ 0.42 34.5 % $ 0.78 65.0 % $ 0.61 51.0 % Return of capital 0.50 42.0 % 0.35 29.5 % 0.08 6.7 % Unrecaptured section 1250 gain 0.28 23.5 % 0.07 5.5 % 0.51 42.3 % Common stock distributions $ 1.20 100.0 % $ 1.20 100.0 % $ 1.20 100.0 % State Income Taxes The Company must pay certain state income taxes, which are included in general and administrative expense on the Company’s Consolidated Statements of Income. The State of Texas gross margins tax on gross receipts from operations is disclosed in the table below as an income tax because it is considered such by the Securities and Exchange Commission. State income tax expense and state income tax payments for the three years ended December 31, 2017 are detailed in the table below: Year Ended December 31, (Dollars in thousands) 2017 2016 2015 State income tax expense: Texas gross margins tax (1) $ 608 $ 562 $ 528 Other — 2 37 Total state income tax expense $ 608 $ 564 $ 565 State income tax payments, net of refunds and collections $ 555 $ 544 $ 758 ______ (1) In the table above, income tax expense for 2015 includes approximately $50 thousand that was recorded to the gain on sale of real estate properties sold, which is included in discontinued operations rather than general and administrative expenses on the Company’s Consolidated Statements of Income.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Fair Value of Financial Instruments The following methods and assumptions were used to estimate the fair value of each class of financial instrument for which it is practical to estimate that value. Cash, cash equivalents and restricted cash - The carrying amount approximates fair value. Mortgage notes receivable - The fair value of mortgage notes receivable is estimated based either on cash flow analyses at an assumed market rate of interest or at a rate consistent with the rates on mortgage notes acquired by the Company recently, if any. Borrowings under the Unsecured Credit Facility due 2020 and Unsecured Term Loan due 2022 - The carrying amount approximates fair value because the borrowings are based on variable market interest rates. Senior unsecured notes payable - The fair value of notes and bonds payable is estimated using cash flow analyses, based on the Company’s current interest rates for similar types of borrowing arrangements. Mortgage notes payable - The fair value is estimated using cash flow analyses, based on the Company’s current interest rates for similar types of borrowing arrangements. Interest rate swap agreements - Interest rate swap agreements are recorded in other liabilities on the Company's Consolidated Balance Sheets at fair value. Fair value is estimated by utilizing pricing models that consider forward yield curves and discount rates. The table below details the fair value and carrying values for notes and bonds payable as of December 31, 2017 and 2016 . December 31, 2017 December 31, 2016 (Dollars in millions) Carrying Value Fair Value Carrying Value Fair Value Notes and bonds payable (1) $ 1,283.9 $ 1,269.7 $ 1,264.4 $ 1,265.1 ______ (1) Level 2 – model-derived valuations in which significant inputs and significant value drivers are observable in active markets.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (unaudited)	12 Months Ended
	Dec. 31, 2017
Selected Quarterly Financial Information [Abstract]
Selected Quarterly Financial Data (unaudited)	Selected Quarterly Financial Data (unaudited) Quarterly financial information for the year ended December 31, 2017 is summarized below. Quarter Ended (Dollars in thousands, except per share data) March 31 (1) June 30 (2) September 30 (3) December 31 (4) 2017 Revenues from continuing operations $ 104,569 $ 105,245 $ 106,953 $ 107,731 Income (loss) from continuing operations 31,858 25,224 3,165 (37,151 ) Income (loss) from discontinued operations (13 ) — 8 — Net income (loss) attributable to common stockholders $ 31,845 $ 25,224 $ 3,173 $ (37,151 ) Net income attributable to common stockholders per share: Basic earnings per common share $ 0.28 $ 0.22 $ 0.02 $ (0.31 ) Diluted earnings per common share $ 0.28 $ 0.22 $ 0.02 $ (0.31 ) ______ (1) The increases in net income and amounts per share for the first quarter of 2017 are primarily attributable to gains of $23.4 million on the sale of six properties. (2) The increases in net income and amounts per share for the second quarter of 2017 are primarily attributable to gains of $16.1 million on the sale of three properties. (3) The decreases in net income and amounts per share for the third quarter of 2017 are primarily attributable to impairment charges of $5.1 million . (4) The decreases in net income and amounts per share for the fourth quarter of 2017 are primarily attributable to a loss on the extinguishment of debt of $45.0 million . Quarterly financial information for the year ended December 31, 2016 is summarized below. Quarter Ended (Dollars in thousands, except per share data) March 31 June 30 September 30 December 31 (1) 2016 Revenues from continuing operations $ 100,021 $ 102,642 $ 103,659 $ 105,309 Income from continuing operations 9,163 12,157 11,857 52,580 Loss from discontinued operations (7 ) (12 ) (23 ) (143 ) Net income attributable to common stockholders $ 9,156 $ 12,145 $ 11,834 $ 52,437 Net income attributable to common stockholders per share: Basic earnings per common share $ 0.09 $ 0.12 $ 0.10 $ 0.46 Diluted earnings per common share $ 0.09 $ 0.12 $ 0.10 $ 0.45 ______ (1) The increases in net income and amounts per share for the fourth quarter of 2016 are primarily attributable to gains of $41.0 million on the sale of six properties.

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2017
Valuation and Qualifying Accounts [Abstract]
Valuation and Qualifying Accounts	Schedule II – Valuation and Qualifying Accounts for the years ended December 31, 2017 , 2016 and 2015 (Dollars in thousands) Balance at Beginning of Period Additions and Deductions Uncollectible Accounts Written-off Balance at End of Period Description Charged /(Credited) to Costs and Expenses Charged to Other Accounts 2017 Accounts and notes receivable allowance $ 148 $ 159 $ — $ 51 $ 256 2016 Accounts and notes receivable allowance $ 179 $ (21 ) $ — $ 10 $ 148 2015 Accounts and notes receivable allowance $ 465 $ (194 ) $ — $ 92 $ 179

Schedule III - Real Estate and

Schedule III - Real Estate and Accumulated Depreciation	12 Months Ended
	Dec. 31, 2017
SEC Schedule III, Real Estate and Accumulated Depreciation Disclosure [Abstract]
Real Estate and Accumulated Depreciation	Schedule III – Real Estate and Accumulated Depreciation as of December 31, 2017 (Dollars in thousands) Land (1) Buildings, Improvements, Lease Intangibles and CIP (1) Property Type Number of Properties State Initial Investment Cost Capitalized Subsequent to Acquisition Total Initial Investment Cost Capitalized Subsequent to Acquisition Total Personal Property (2) (3) (5) Total Property (1) (3) Accumulated Depreciation (4) Encumbrances Date Acquired Date Constructed Medical office/outpatient 193 AL, AZ, CA, CO, DC, FL, GA, HI, IA, IL, IN, LA, MD, MI, MN, MO, MS, NC, OH, OK, SC, SD, TN, TX, VA, WA $ 190,813 $ 3,862 $ 194,675 $ 2,823,611 $ 502,564 $ 3,326,175 $ 4,193 $ 3,525,043 $ 835,768 $ 154,916 1993-2017 1906 -2015 Inpatient 6 CA, CO, MO, PA, TX 8,179 — 8,179 255,495 9,861 265,356 — 273,535 66,780 — 1994-2013 1986 -2013 Other 10 IA, MI, TN, TX, VA 2,992 73 3,065 66,440 7,143 73,583 600 77,248 26,032 — 1993-2015 1964 - 2015 Total Real Estate 209 201,984 3,935 205,919 3,145,546 519,568 3,665,114 4,793 3,875,826 928,580 154,916 Land Held for Develop. — 20,123 — 20,123 — — — — 20,123 239 — Construction in Progress (5) — — — — — — 5,458 — 5,458 — — Corporate Property — — — — — — — 5,603 5,603 4,401 — Total Properties 209 $ 222,107 $ 3,935 $ 226,042 $ 3,145,546 $ 519,568 $ 3,670,572 $ 10,396 $ 3,907,010 $ 933,220 $ 154,916 (1) Includes eight assets held for sale as of December 31, 2017 of approximately $68.4 million (gross) and accumulated depreciation of $35.8 million . (2) Total properties as of December 31, 2017 have an estimated aggregate total cost of $ 4.0 billion for federal income tax purposes. (3) Depreciation is provided for on a straight-line basis on buildings and improvements over 3.3 to 39.0 years , lease intangibles over to 2.1 to 99.0 years , personal property over 2.8 to 20.0 years, and land improvements over 5.0 to 39.0 years. (4) Includes unamortized premium of $2.7 million and unaccreted discount of $1.3 million and issuance costs of $0.9 million as of December 31, 2017 . (5) Rollforward of Total Property and Accumulated Depreciation for the year ended December 31, 2017 , 2016 and 2015 follows: Year Ended December 31, 2017 Year Ended December 31, 2016 Year Ended December 31, 2015 (Dollars in thousands) Total Property Accumulated Depreciation Total Property Accumulated Depreciation Total Property Accumulated Depreciation Beginning Balance $ 3,633,993 $ 843,816 $ 3,382,680 $ 762,996 $ 3,271,536 $ 705,135 Additions during the period: Real Estate acquired 322,616 4,206 239,265 3,898 183,478 3,048 Other improvements 59,442 135,807 70,595 121,592 47,985 111,625 Land held for development — 74 — 26 500 26 Construction in Progress 14,598 — 35,596 — 19,024 — Retirement/dispositions: Real Estate (123,639 ) (50,683 ) (94,143 ) (44,696 ) (139,741 ) (56,838 ) Land held for development — — — — (102 ) — Ending Balance $ 3,907,010 $ 933,220 $ 3,633,993 $ 843,816 $ 3,382,680 $ 762,996

Schedule IV - Mortgage Loans on

Schedule IV - Mortgage Loans on Real Estate	12 Months Ended
	Dec. 31, 2017
Mortgage Loans on Real Estate [Abstract]
Mortgage Loans on Real Estate	Schedule IV – Mortgage Loans on Real Estate as of December 31, 2017 The Company had no mortgage notes receivable outstanding as of December 31, 2017 . A rollforward of mortgage loans on real estate for the three years ended December 31, 2017 follows: Year Ended December 31, (Dollars in thousands) 2017 2016 2015 Balance at beginning of period $ — $ — $ 1,900 Deductions during period: Principal repayments and reductions (1) — — (1,900 ) — — (1,900 ) Balance at end of period $ — $ — $ — (1) Principal repayments for the year ended December 31, 2015 includes unscheduled principal reductions on the mortgage note of $1.9 million .

Summary of Significant Accoun30

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Business Overview	Business Overview Healthcare Realty Trust Incorporated (the “Company”) is a real estate investment trust ("REIT") that owns, leases, manages, acquires, finances, develops and redevelops income-producing real estate properties associated primarily with the delivery of outpatient healthcare services throughout the United States of America. The Company had gross investments of approximately $3.8 billion in 201 real estate properties, construction in progress, land held for development and corporate property as of December 31, 2017 . The Company’s 201 owned real estate properties are located in 27 states and total approximately 14.6 million square feet. The Company provided property management services to approximately 11.5 million square feet nationwide. Square footage and property count disclosures in this Annual Report on Form 10-K are unaudited.
Principles of Consolidation	Principles of Consolidation The Consolidated Financial Statements include the accounts of the Company, its wholly owned subsidiaries, joint ventures, partnerships and consolidated variable interest entities (“VIE”) where the Company controls the operating activities of the VIE. In accordance with the consolidation accounting standards, the Company must evaluate each contractual relationship it has with its lessees, borrowers, or others to determine whether or not the contractual arrangement creates a variable interest in those entities. If the Company determines that it has a variable interest and the entity is a VIE, then management must determine whether or not the Company is the primary beneficiary of the VIE, resulting in consolidation of the VIE if the Company is the primary beneficiary. A primary beneficiary has the power to direct those activities of the VIE that most significantly impact its economic performance and has the obligation to absorb the losses of, or receive the benefits from, the VIE. The Company had no VIEs as of December 31, 2017 and 2016 . The Company's investments in its unconsolidated joint ventures are included in other assets and the related equity income is recognized in other income (expense) on the Company's Consolidated Financial Statements. See Note 7 for additional information. All significant intercompany accounts, transactions and balances have been eliminated upon consolidation in the Consolidated Financial Statements.
Use of Estimates in the Consolidated Financial Statements	Use of Estimates in the Consolidated Financial Statements Preparation of the Consolidated Financial Statements in accordance with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect amounts reported in the Consolidated Financial Statements and accompanying notes. Actual results may differ from those estimates.
Segment Reporting	Segment Reporting The Company owns, leases, acquires, manages, finances, develops and redevelops outpatient and other healthcare-related properties. The Company is managed as one reporting unit, rather than multiple reporting units, for internal reporting purposes and for internal decision-making. Therefore, the Company discloses its operating results in a single reportable segment.
Real Estate Properties	Real Estate Properties Real estate properties are recorded at cost or at fair value if acquired in a transaction that is a business combination under Accounting Standards Codification Topic 805, Business Combinations . Cost or fair value at the time of acquisition is allocated among land, buildings, tenant improvements, lease and other intangibles, and personal property as applicable. The Company’s gross real estate assets, on a financial reporting basis, totaled approximately $3.8 billion as of December 31, 2017 and $3.6 billion as of December 31, 2016 . During 2017 and 2016 , the Company eliminated against accumulated depreciation approximately $10.2 million and $6.7 million , respectively, of fully amortized real estate intangibles that were initially recorded as a component of certain real estate acquisitions. Also during 2017 and 2016 , approximately $2.6 million and $0.1 million of fully depreciated tenant and capital improvements that were no longer in service were eliminated against accumulated depreciation. Depreciation expense for the three years ended December 31, 2017, 2016 and 2015 was $129.4 million , $116.5 million and $106.5 million , respectively. Depreciation and amortization of real estate assets and liabilities in place as of December 31, 2017 , is provided for on a straight-line basis over the asset’s estimated useful life: Land improvements 5.0 to 39.0 years Buildings and improvements 3.3 to 39.0 years Lease intangibles (including ground lease intangibles) 2.1 to 99.0 years Personal property 2.8 to 20.0 years The Company capitalizes direct costs, including costs such as construction costs and professional services, and indirect costs, including capitalized interest and overhead costs, associated with the development and construction of real estate assets while substantive activities are ongoing to prepare the assets for their intended use. Capitalized interest cost is calculated using the weighted average interest rate of the Company's unsecured debt or the interest rate on project specific debt, if applicable. The Company continues to capitalize interest on the unoccupied portion of the properties in stabilization for up to one year after the buildings have been placed into service, at which time the capitalization of interest must cease.
Land Held for Development	Land Held for Development Land held for development includes parcels of land owned by the Company, upon which the Company intends to develop and own outpatient healthcare facilities. The Company’s investment in six parcels of land held for development located adjacent to certain of the Company's existing medical office buildings in Texas, Iowa and Tennessee totaled approximately $20.1 million as of December 31, 2017 and 2016
Asset Impairment	Assets Held for Sale Long-lived assets held for sale are reported at the lower of their carrying amount or their fair value less cost to sell estimate. Further, depreciation of these assets ceases at the time the assets are classified as held for sale. Losses resulting from the sale of such properties are characterized as impairment losses in the Consolidated Statements of Income. Asset Impairment The Company assesses the potential for impairment of identifiable, definite-lived, intangible assets and long-lived assets, including real estate properties, whenever events occur or a change in circumstances indicates that the carrying value might not be fully recoverable. Indicators of impairment may include significant underperformance of an asset relative to historical or expected operating results; significant changes in the Company’s use of assets or the strategy for its overall business; plans to sell an asset before its depreciable life has ended; the expiration of a significant portion of leases in a property; or significant negative economic trends or negative industry trends for the Company or its operators. In addition, the Company reviews for possible impairment, those assets subject to purchase options and those impacted by casualties, such as tornadoes and hurricanes. If management determines that the carrying value of the Company’s assets may not be fully recoverable based on the existence of any of the factors above, or others, management would measure and record an impairment charge based on the estimated fair value of the property or the estimated fair value less costs to sell the property.
Acquisitions of Real Estate Properties with In-Place Leases	Acquisitions of Real Estate Properties with In-Place Leases Acquisitions of real estate properties with in-place leases are accounted for at relative fair value. When a building with in-place leases is acquired, the cost of the acquisition must be allocated between the tangible real estate assets "as-if-vacant" and the intangible real estate assets related to in-place leases based on their estimated fair values. Where appropriate, the intangible assets recorded could include goodwill or customer relationship assets. The values related to above- or below-market in-place lease intangibles are amortized over the remaining term of the leases upon acquisition to rental income where the Company is the lessor and to property operating expense where the Company is the lessee, and are amortized over the remaining term of the leases upon acquisition. The Company considers whether any of the in-place lease rental rates are above- or below-market. An asset (if the actual rental rate is above-market) or a liability (if the actual rental rate is below-market) is calculated and recorded in an amount equal to the present value of the future cash flows that represent the difference between the actual lease rate and the average market rate. If an in-place lease is identified as a below-market rental rate, the Company would also evaluate any renewal options associated with that lease to determine if the intangible should include those periods. The Company also estimates an absorption period, which can vary by property, assuming the building is vacant and must be leased up to the actual level of occupancy when acquired. During that absorption period, the owner would incur direct costs, such as tenant improvements, and would suffer lost rental income. Likewise, the owner would have acquired a measurable asset in that, assuming the building was vacant, certain fixed costs would be avoided because the actual in-place lessees would reimburse a certain portion of fixed costs through expense reimbursements during the absorption period. All of these intangible assets (above- or below-market lease, tenant improvement costs avoided, leasing costs avoided, rental income lost, and expenses recovered through in-place lessee reimbursements) are estimated and recorded in amounts equal to the present value of estimated future cash flows. The actual purchase price is allocated based on the various asset fair values described above. The building and tenant improvement components of the purchase price are depreciated over the estimated useful life of the building or the weighted average remaining term of the in-places leases. The at-market, in-place lease intangibles are amortized to amortization expense over the weighted average remaining term of the leases, customer relationship assets are amortized to amortization expense over terms applicable to each acquisition, and any goodwill recorded would be reviewed for impairment at least annually. The fair values of at-market in-place lease and other intangible assets are amortized and reflected in amortization expense in the Company’s Consolidated Statements of Income. See Note 8 for more details on the Company’s intangible assets.
Fair Value Measurements	Fair Value Measurements Fair value is defined as the price that would be received to sell an asset, or paid to transfer a liability, in an orderly transaction between market participants. In calculating fair value, a company must maximize the use of observable market inputs, minimize the use of unobservable market inputs and disclose in the form of an outlined hierarchy the details of such fair value measurements. A hierarchy of valuation techniques is defined to determine whether the inputs to a fair value measurement are considered to be observable or unobservable in a marketplace. Observable inputs reflect market data obtained from independent sources, while unobservable inputs reflect the Company’s market assumptions. This hierarchy requires the use of observable market data when available. These inputs have created the following fair value hierarchy: • Level 1 – quoted prices for identical instruments in active markets; • Level 2 – quoted prices for similar instruments in active markets; quoted prices for identical or similar instruments in markets that are not active; and model-derived valuations in which significant inputs and significant value drivers are observable in active markets; and • Level 3 – fair value measurements derived from valuation techniques in which one or more significant inputs or significant value drivers are unobservable. Executed purchase and sale agreements, that are binding agreements, are categorized as level one inputs. Brokerage estimates, letters of intent, or unexecuted purchase and sale agreements are considered to be level three as they are nonbinding in nature. During 2017 , in connection with the sale of a medical office building, the Company recorded an impairment charge in continuing operations of approximately $5.1 million based on the contractual sales price, a level one input. The Company used level one inputs to record an impairment charge in continuing operations of approximately $0.3 million related to another property sold during 2017, reducing the Company's carrying value to the estimated fair value of the property less costs to sell prior to sale.
Fair Value of Derivative Financial Instruments	Fair Value of Derivative Financial Instruments Derivative financial instruments are recorded at fair value on the Company's Consolidated Balance Sheets as other assets or other liabilities. The valuation of derivative instruments requires the Company to make estimates and judgments that affect the fair value of the instruments. Fair values of derivatives are estimated by pricing models that consider the forward yield curves and discount rates. The fair value of the Company's forward starting interest rate swap contracts are estimated by pricing models that consider foreign trade rates and discount rates. Such amounts and the recognition of such amounts are subject to significant estimates that may change in the future. For derivatives designated in qualifying cash flow hedging relationships, the change in fair value of the effective portion of the derivatives is recognized in accumulated other comprehensive income (loss). Gains and losses are reclassified from accumulated other comprehensive income (loss) into earnings once the underlying hedged transaction is recognized in earnings. As of December 31, 2017 and 2016, the Company had $1.3 million and $1.4 million , respectively recorded in accumulated other comprehensive loss related to forward starting interest rate swaps entered into and settled during 2015 and a hedge of the Company's variable rate debt.
Cash and Cash Equivalents	Cash, Cash Equivalents and Restricted Cash Cash and cash equivalents includes short-term investments with original maturities of three months or less when purchased. Restricted cash includes cash held in escrow in connection with proceeds from the sales of certain real estate properties. The carrying amount approximates fair value due to the short term maturity of these investments.
Allowance for Doubtful Accounts and Credit Losses	Allowance for Doubtful Accounts and Credit Losses Accounts Receivable Management monitors the aging and collectibility of its accounts receivable balances on an ongoing basis. Whenever deterioration in the timeliness of payment from a tenant or sponsoring health system is noted, management investigates and determines the reason or reasons for the delay. Considering all information gathered, management’s judgment is exercised in determining whether a receivable is potentially uncollectible and, if so, how much or what percentage may be uncollectible. Among the factors management considers in determining collectibility are: the type of contractual arrangement under which the receivable was recorded (e.g., a triple net lease, a gross lease, a property operating agreement, or some other type of agreement); the tenant’s reason for slow payment; industry influences under which the tenant operates; evidence of willingness and ability of the tenant to pay the receivable; credit-worthiness of the tenant; collateral, security deposit, letters of credit or other monies held as security; tenant’s historical payment pattern; other contractual agreements between the tenant and the Company; relationship between the tenant and the Company; the state in which the tenant operates; and the existence of a guarantor and the willingness and ability of the guarantor to pay the receivable. Considering these factors and others, management concludes whether all or some of the aged receivable balance is likely uncollectible. Upon determining that some portion of the receivable is likely uncollectible, the Company records a provision for bad debts for the amount it expects will be uncollectible. When efforts to collect a receivable are exhausted, the receivable amount is charged off against the allowance. The Company does not hold any accounts receivable for sale. Mortgage Notes The Company had no mortgage notes receivable outstanding as of December 31, 2017 and 2016 and no allowances were recorded on mortgage notes receivables during 2017 or 2016 . The Company evaluates collectibility of any mortgage notes and records allowances on the notes as necessary. A loan is impaired when it is probable that a creditor will be unable to collect all amounts due according to the contractual terms of the loan as scheduled, including both contractual interest and principal payments. This assessment also includes an evaluation of the loan collateral. If a mortgage loan becomes past due, the Company will review the specific circumstances and may discontinue the accrual of interest on the loan. The loan is not returned to accrual status until the debtor has demonstrated the ability to continue debt service in accordance with the contractual terms. Loans placed on non-accrual status will be accounted for either on a cash basis, in which income is recognized only upon receipt of cash, or on a cost-recovery basis, in which all cash receipts reduce the carrying value of the loan, based on the Company’s expectation of future collectibility.
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets Goodwill and intangible assets with indefinite lives are not amortized, but are tested at least annually for impairment. Intangible assets with finite lives are amortized over their respective lives to their estimated residual values and are reviewed for impairment only when impairment indicators are present. Identifiable intangible assets of the Company are comprised of enterprise goodwill, in-place lease intangible assets, customer relationship intangible assets, and deferred financing costs. In-place lease and customer relationship intangible assets are amortized on a straight-line basis over the applicable lives of the assets. Deferred financing costs are amortized over the term of the related credit facility or other debt instrument under the straight-line method, which approximates amortization under the effective interest method. Goodwill is not amortized but is evaluated annually as of December 31 for impairment. Both the 2017 and 2016 impairment evaluations indicated that no impairment had occurred with respect to the $3.5 million goodwill asset.
Contingent Liabilities	Contingent Liabilities From time to time, the Company may be subject to loss contingencies arising from legal proceedings and similar matters. Additionally, while the Company maintains comprehensive liability and property insurance with respect to each of its properties, the Company may be exposed to unforeseen losses related to uninsured or underinsured damages. The Company continually monitors any matters that may present a contingent liability, and, on a quarterly basis, management reviews the Company’s reserves and accruals in relation to each of them, adjusting provisions as necessary in view of changes in available information. Liabilities for contingencies are first recorded when a loss is determined to be both probable and can be reasonably estimated. Changes in estimates regarding the exposure to a contingent loss are reflected as adjustments to the related liability in the periods when they occur. Because of uncertainties inherent in the estimation of contingent liabilities, it is possible that the Company’s provision for contingent losses could change materially in the near term. To the extent that any significant losses, in addition to amounts recognized, are at least reasonably possible, such amounts will be disclosed in the notes to the Consolidated Financial Statements.
Stock-based Compensation	Stock-Based Compensation The Company has various employee and director stock-based awards outstanding. These awards include non-vested common stock and options to purchase common stock granted to employees pursuant to the 2015 Stock Incentive Plan and its predecessor plans (the “2015 Incentive Plan”) and the 2000 Employee Stock Purchase Plan (the “Employee Stock Purchase Plan”). The Company recognizes share-based payments to employees and directors in the Consolidated Statements of Income on a straight-line basis over the requisite service period based on the fair value of the award on the measurement date. The Employee Stock Purchase Plan features a “look-back” provision which enables the employee to purchase a fixed number of common shares at the lesser of 85% of the market price on the date of grant or 85% of the market price on the date of exercise, with optional purchase dates occurring once each quarter for 27 months . The Company accounts for awards to its employees under the Employee Stock Purchase Plan based on fair value, using the Black-Scholes model, and generally recognizes expense over the award’s vesting period, net of estimated forfeitures. Since the options granted under the Employee Stock Purchase Plan immediately vest, the Company records compensation expense for those options when they are granted in the first quarter of each year and then may record additional compensation expense in subsequent quarters as warranted. In each of the years ended December 31, 2017 , 2016 and 2015 , the Company recognized in general and administrative expenses approximately $0.2 million of compensation expense related to the annual grant of options to its employees to purchase shares under the Employee Stock Purchase Plan.
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Certain items must be included in comprehensive income, including items such as foreign currency translation adjustments, minimum pension liability adjustments, derivative instruments and unrealized gains or losses on available-for-sale securities. The Company’s accumulated other comprehensive income (loss) as of December 31, 2017 consists of the loss for changes in the fair value of active derivatives designated as cash flow hedges and the loss on the unamortized settlement of four forward starting swaps. As of December 31, 2016, the Company's accumulated other comprehensive income (loss) consisted only of the loss on the unamortized settlement of four forward starting swaps.
Revenue Recognition	Revenue Recognition The Company recognizes revenue when it is realized or realizable and earned. There are four criteria that must all be met before a Company may recognize revenue, including that persuasive evidence that an arrangement exists, delivery has occurred or services have been rendered (i.e., the tenant has taken possession of and controls the physical use of the leased asset), the price has been fixed or is determinable, and collectibility is reasonably assured. Income received but not yet earned is deferred until such time it is earned. Deferred revenue, included in other liabilities on the Consolidated Balance Sheets, was $36.0 million and $32.4 million , respectively, as of December 31, 2017 and 2016 which includes deferred tenant improvement reimbursements of $20.1 million and $20.6 million , respectively, which will be recognized as revenue over the life of each respective lease. The Company derives most of its revenues from its real estate property portfolio. The Company’s rental and mortgage interest income is recognized based on contractual arrangements with its tenants, sponsoring health systems or borrowers. These contractual arrangements fall into three categories: leases, mortgage notes receivable, and property operating agreements as described in the following paragraphs. The Company may accrue late fees based on the contractual terms of a lease or note. Such fees, if accrued, are included in rental income or mortgage interest income on the Company’s Consolidated Statements of Income, based on the type of contractual agreement. Rental Income Rental income related to non-cancelable operating leases is recognized as earned over the life of the lease agreements on a straight-line basis. The Company's lease agreements generally include provisions for stated annual increases or increases based on a Consumer Price Index ("CPI"). Rental income from properties under multi-tenant office lease arrangements and rental income from properties with single-tenant lease arrangements are included in rental income on the Company's Consolidated Statements of Income. The components of rental income are as follows: Year Ended December 31, (Dollars in thousands) 2017 2016 2015 Property operating income $ 363,907 $ 336,409 $ 306,550 Single-tenant net lease 52,873 63,871 67,238 Straight-line rent 6,072 7,201 9,545 Rental income $ 422,852 $ 407,481 $ 383,333 Operating expense recoveries, included in property operating income, were approximately $73.4 million , $66.0 million and $58.9 million , respectively, for the years ended December 31, 2017 , 2016 and 2015 . Mortgage Interest Income Interest income on the Company’s mortgage notes receivable is recognized based on the interest rates, maturity dates and amortization periods in accordance with each note agreement. The Company has no outstanding mortgage notes receivable as of December 31, 2017 , 2016 and 2015. The Company amortizes any fees paid related to its mortgage notes receivable to mortgage interest income over the term of the loan on a straight-line basis which approximates amortization under the effective interest method.
Other operating income	Other Operating Income Other operating income on the Company’s Consolidated Statements of Income was comprised of the following: Year Ended December 31, (Dollars in thousands) 2017 2016 2015 Property lease guaranty revenue $ 726 $ 3,058 $ 3,890 Interest income 361 473 579 Management fee income 276 369 370 Other 284 249 208 $ 1,647 $ 4,149 $ 5,047 One , two and five of the Company’s owned real estate properties as of December 31, 2017 , 2016 and 2015, respectively, were covered under property operating agreements between the Company and a sponsoring health system, which contractually obligate the sponsoring health system to provide to the Company a minimum return on the Company’s investment in the property in exchange for the right to be involved in the operating decisions of the property, including tenancy. If the minimum return is not achieved through normal operations of the property, the Company calculates and accrues to property lease guaranty revenue, each quarter, any shortfalls due from the sponsoring health systems under the terms of the property operating agreement. Interest income generally relates to interest on tenant improvement reimbursements as defined in each note or lease agreement. Management fees for property management services provided to third parties are generally calculated, accrued and billed monthly based on a percentage of cash collections of tenant receivables for the month or a stated amount per square foot. Internal management fee income, where the Company manages its owned properties, is eliminated in consolidation.
Federal Income Taxes	Federal Income Taxes No provision has been made for federal income taxes. The Company intends at all times to qualify as a REIT under Sections 856 through 860 of the Internal Revenue Code. The Company must distribute at least 90% per annum of its real estate investment trust taxable income to its stockholders and meet other requirements to continue to qualify as a real estate investment trust. See Note 16 for further discussion. The Company classifies interest and penalties related to uncertain tax positions, if any, in the Consolidated Financial Statements as a component of general and administrative expenses. No such amounts were recognized during the three years ended December 31, 2017. Federal tax returns for the years 2014, 2015 , 2016 and 2017 are currently subject to examination by taxing authorities.
State Income Taxes	State Income Taxes The Company must pay certain state income taxes and the provisions for such taxes are generally included in general and administrative expense on the Company’s Consolidated Statements of Income.
Sales and Use Taxes	Sales and Use Taxes The Company must pay sales and use taxes to certain state tax authorities based on rents collected from tenants in properties located in those states. The Company is generally reimbursed for these taxes by the tenant. The Company accounts for the payments to the taxing authority and subsequent reimbursement from the tenant on a net basis in revenues in the Company’s Consolidated Statements of Income.
Discontinued Operations	Discontinued Operations The Company sells properties from time to time due to a variety of factors, including among other things, market conditions or the exercise of purchase options by tenants. The Company does not expect these dispositions to meet the amended definition of a discontinued operation as defined in Accounting Standards Update ("ASU") No. 2014-08, "Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity." The Company adopted ASU No. 2014-08 on a prospective basis beginning January 1, 2015 which excluded properties previously in discontinued operations prior to adoption. However, if a sale were to meet the amended definition representing a strategic shift that has or will have a major effect on the Company's operations and financial results, the operating results of the properties that have been sold or are held for sale will be reported as discontinued operations in the Company’s Consolidated Statements of Income for all periods presented.
Earning Per Share	Earnings per Share The Company uses the two-class method of computing net earnings per common share. Earnings per common share is calculated by considering share-based payment awards that contain nonforfeitable rights to dividends or dividend equivalents as participating securities. Undistributed earnings (excess net income over dividend payments) are allocated on a prorata basis to common shareholders and restricted shareholders. Undistributed losses (dividends in excess of net income) do not get allocated to restricted stockholders as they do not have the contractual obligation to share in losses. The amount of undistributed losses that applies to the restricted stockholders is allocated to the common stockholder. Basic earnings per common share is calculated using weighted average shares outstanding less issued and outstanding non-vested shares of common stock. Diluted earnings per common share is calculated using weighted average shares outstanding plus the dilutive effect of the outstanding stock options from the Employee Stock Purchase Plan using the treasury stock method and the average stock price during the period.
Reclassifications	Reclassifications Condensed Consolidated Statements of Income Certain reclassifications have been made on the Company's Condensed Consolidated Statements of Income. The Company reclassified acquisition and pursuit costs from the general and administrative line item to a separate line item. The acquisition and pursuit costs line item includes direct third party and travel costs related to the Company's pursuit of acquisitions and developments. In addition, the Company combined the line items labeled depreciation and amortization into one line item.
New Accounting Pronouncements	New Accounting Pronouncements Accounting Standards Update No. 2014-09 and No. 2015-14 In May 2014, the Financial Accounting Standards Board ("FASB") issued ASU No. 2014-09, "Revenue from Contracts with Customers," a comprehensive new revenue recognition standard that supersedes most existing revenue recognition guidance, including sales of real estate. This standard's core principle is that a company will recognize revenue when it transfers goods or services to customers in amounts that reflect the consideration to which the company expects to be entitled in exchange for those goods and services. However, leasing contracts, representing the major source of the Company's revenues, are not within the scope of the new standard and will continue to be accounted for under other standards. In August 2015, the FASB issued ASU No. 2015-14, "Revenue from Contracts with Customers (Topic 606); Deferral of the Effective Date." This standard is effective for the Company for annual and interim periods beginning after December 15, 2017. The Company adopted this standard by using the full retrospective adoption method beginning on January 1, 2018. The Company's revenue-producing contracts are primarily leases that are not within the scope of this standard. As a result, the adoption of this standard did not have a material impact on the timing and measurement of the Company's leasing revenues. The Company has identified that parking income, rental lease guaranty income and management fee income will be within the scope of Topic 606. However, these items were determined to have the same pattern of revenue recognition that the Company had historically recognized. The Company reclassified these amounts along with all other items that are accounted for within the scope of Topic 606 into the Other operating line item on the Company's Consolidated Statements of Income. This line item historically contained the revenue associated with rental lease guaranty income, management fee income and other non-lease revenue. The Company reclassified parking income from rental income to other operating income. The following table represents the impact of the adoption of this standard on the Company's Consolidated Statements of Income for the years ended December 31, 2017 and 2016: Year Ended December 31, 2017 2016 (in thousands) As Reported As Reclassified As Previously Reported As Reclassified REVENUES Rental income $ 422,852 $ 416,727 $ 407,481 $ 401,989 Other operating 1,647 8,011 4,149 9,966 $ 424,499 $ 424,738 $ 411,630 $ 411,955 OTHER INCOME (EXPENSE) Interest and other income, net $ 896 $ 658 $ 375 $ 50 INCOME FROM CONTINUING OPERATIONS $ 23,096 $ 23,096 $ 85,756 $ 85,756 Accounting Standards Update No. 2016-02 In February 2016, the FASB issued ASU No. 2016-02, "Leases." For lessees, the new standard establishes a right-of-use ("ROU") model that requires a lessee to record a ROU asset and a lease liability on the balance sheet for all leases with terms longer than 12 months. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. The Company expects that all of the leases where the Company is the lessee will be recorded on the Company's balance sheet. See Note 15 for a discussion of leases where the Company is the lessee. For lessors, the new standard requires a lessor to classify leases as either sales-type, finance or operating. A lease will be treated as a sale if it transfers all of the risks and rewards, as well as control of the underlying asset, to the lessee. If risks and rewards are conveyed without the transfer of control, the lease is treated as financing. If the lessor doesn't convey risks and rewards or control, then the lease would be classified as an operating lease. The Company has historically only entered into operating leases. The new standard is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years with early adoption permitted. A modified retrospective transition approach is required for lessors for sales-type, direct financing, and operating leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements, with certain practical expedients available. The Company is evaluating the impact from the adoption of this new standard on the Consolidated Financial Statements and related notes. Accounting Standards Update No. 2016-13 In June 2016, the FASB issued ASU 2016-13, "Measurement of Credit Losses on Financial Instruments." This update is intended to improve financial reporting by requiring timelier recognition of credit losses on loans and other financial instruments that are not accounted for at fair value through net income, including loans held for investment, held-to-maturity debt securities, trade and other receivables, net investment in leases and other such commitments. This update requires that financial statement assets measured at an amortized cost and certain other financial instruments be presented at the net amount expected to be collected, through an allowance for credit losses that is deducted from the amortized cost basis. This standard is effective for annual and interim periods beginning after December 15, 2019 with early adoption permitted. The Company is in the initial stages of evaluating the impact from the adoption of this new standard on the Consolidated Financial Statements and related notes. Accounting Standards Update No. 2016-15 In August 2016, the FASB issued ASU No. 2016-15, "Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments." This update clarifies whether the following items should be classified as operating, investing or financing in the statement of cash flows: (i) debt prepayments and extinguishment costs, (ii) settlement of zero-coupon debt, (iii) settlement of contingent consideration, (iv) insurance proceeds, (v) settlement of corporate-owned life insurance and bank-owned life insurance policies, (vi) distributions from equity method investees, (vii) beneficial interest in securitization transactions and (viii) receipts and payments with aspects of more than one class of cash flows. This standard is effective for the Company for annual and interim periods beginning on January 1, 2018 with early adoption permitted on a retrospective transition method to each period presented. The Company adopted this standard effective January 1, 2017. In connection with the adoption of this update, the Company elected to use the cumulative earnings approach to classify distributions when received related to the Company's equity method investments. There was not a material impact on the Company's Consolidated Financial Statements and related notes resulting from the adoption of this standard. However, the Company made the following reclassification of accrued interest related to the early extinguishment of debt on its Statements of Cash Flows for the year ended December 31, 2015: Year Ended December 31, 2015 (in thousands) As Previously Reported As Reclassified Cash flows used in financing activities $ (94,010 ) $ (87,618 ) Cash flows provided by operating activities $ 160,375 $ 153,983 Accounting Standards Update No. 2017-01 In January 2017, the FASB issued ASU No. 2017-01, "Business Combinations: Clarifying the Definition of a Business." This update modifies the requirements to meet the definition of a business under Topic 805, "Business Combinations." The amendments provide a screen to determine when an integrated 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 group of similar identifiable assets, the set is not a business. The Company believes that this amendment will result in most of its real estate acquisitions being accounted for as asset acquisitions rather than business combinations. This standard is effective for the Company for annual and interim periods beginning after December 15, 2017 with early adoption permitted. The Company adopted this standard effective January 1, 2017 and has accounted for acquisitions that occurred during the year as asset acquisitions. The impact to the Consolidated Financial Statements and related notes as a result of the adoption of this standard is primarily related to the difference in the accounting of acquisition costs. When accounting for these costs as a part of an asset acquisition, the Company will be permitted to capitalize the costs. The adoption of this standard did not have a material impact on the Consolidated Financial Statements and related notes. Accounting Standards Update No. 2017-04 In January 2017, the FASB issued ASU 2017-04, "Simplifying the Test for Goodwill Impairment." This update eliminates Step 2 of the goodwill impairment test. As such, an entity will perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity should recognize a goodwill impairment charge for the amount by which the reporting unit's carrying amount exceeds its fair value. This standard is effective for the Company for annual and interim periods beginning after December 15, 2019. The Company does not expect a material impact on the Consolidated Financial Statements and related notes from the adoption of this standard. Accounting Standards Update No. 2017-05 In February 2017, the FASB issued ASU 2017-05, "Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets." This update defines an in-substance nonfinancial asset, unifies guidance related to partial sales of nonfinancial assets, eliminates rules specifically addressing the sales of real estate, removes exception to the financial asset derecognition model and clarifies the accounting for contributions of nonfinancial assets to joint ventures. This standard is effective for the Company for annual and interim periods beginning after December 15, 2017 with early adoption permitted. The Company adopted this standard as of January 1, 2018 on the full retrospective adoption method. However, there was no impact to the Company's Consolidated Financial Statements from the adoption of this standard. Accounting Standards Update No. 2017-09 In May 2017, the FASB issued ASU 2017-09, "Compensation - Stock Compensation - Scope of Modification Accounting." This update provides guidance about which changes to the terms and conditions of share-based awards require an entity to apply modification accounting in Topic 718. This standard is effective for the Company for the annual and interim periods beginning after December 15, 2017 with early adoption permitted. The Company adopted this standard on January 1, 2018. The Company does not expect a material impact to the Consolidated Financial Statements from the adoption of this standard. Accounting Standards Update No. 2017-12 In August 2017, the FASB issued ASU 2017-12, "Derivatives and Hedging - 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. The transition guidance allows for early adoption of the new standard using a modified retrospective transition method in any interim period after issuance of the update, or alternatively requires adoption for fiscal years beginning after December 15, 2018. The modified retrospective transition method will require the Company to recognize the cumulative effect of initially applying this standard as an adjustment to accumulated other comprehensive income with a corresponding adjustment to the opening balance of retained earnings as of the beginning of the fiscal year that an entity adopts the update. The Company adopted this standard in the fourth quarter of 2017. The Company entered into two interest rate swaps in December 2017 in which the Company elected hedge accounting in compliance with this standard. The Company had no active hedging relationships upon the adoption of this standard and therefore, the adoption of the standard did not have an impact on the Company's Consolidated Financial Statements.

Summary of Significant Accoun31

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Assets' estimated useful life	Depreciation expense for the three years ended December 31, 2017, 2016 and 2015 was $129.4 million , $116.5 million and $106.5 million , respectively. Depreciation and amortization of real estate assets and liabilities in place as of December 31, 2017 , is provided for on a straight-line basis over the asset’s estimated useful life: Land improvements 5.0 to 39.0 years Buildings and improvements 3.3 to 39.0 years Lease intangibles (including ground lease intangibles) 2.1 to 99.0 years Personal property 2.8 to 20.0 years
Schedule of cash and cash equivalents	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Company's Consolidated Balance Sheets with the same amounts shown on the Company's Consolidated Statements of Cash Flows: December 31, (Dollars in thousands) 2017 2016 Cash and cash equivalents $ 6,215 $ 5,409 Restricted cash — 49,098 Total cash, cash equivalents and restricted cash $ 6,215 $ 54,507
Schedule of rental income	The components of rental income are as follows: Year Ended December 31, (Dollars in thousands) 2017 2016 2015 Property operating income $ 363,907 $ 336,409 $ 306,550 Single-tenant net lease 52,873 63,871 67,238 Straight-line rent 6,072 7,201 9,545 Rental income $ 422,852 $ 407,481 $ 383,333
Other operating income	Other operating income on the Company’s Consolidated Statements of Income was comprised of the following: Year Ended December 31, (Dollars in thousands) 2017 2016 2015 Property lease guaranty revenue $ 726 $ 3,058 $ 3,890 Interest income 361 473 579 Management fee income 276 369 370 Other 284 249 208 $ 1,647 $ 4,149 $ 5,047
Schedule of reclassified expenses	These reclassifications are as follows: Year Ended December 31, 2016 2015 (in thousands) As Previously Reported As Reclassified As Previously Reported As Reclassified General and administrative $ 35,805 $ 31,309 $ 26,925 $ 24,716 Acquisition and pursuit costs — 4,496 — 2,209 Total $ 35,805 $ 35,805 $ 26,925 $ 26,925 Depreciation $ 116,483 $ — $ 106,530 $ — Amortization 11,207 — 10,084 — Depreciation and amortization — 127,690 — 116,614 Total $ 127,690 $ 127,690 $ 116,614 $ 116,614
Schedule of previously reported balances	The following table represents the impact of the adoption of this standard on the Company's Consolidated Statements of Income for the years ended December 31, 2017 and 2016: Year Ended December 31, 2017 2016 (in thousands) As Reported As Reclassified As Previously Reported As Reclassified REVENUES Rental income $ 422,852 $ 416,727 $ 407,481 $ 401,989 Other operating 1,647 8,011 4,149 9,966 $ 424,499 $ 424,738 $ 411,630 $ 411,955 OTHER INCOME (EXPENSE) Interest and other income, net $ 896 $ 658 $ 375 $ 50 INCOME FROM CONTINUING OPERATIONS $ 23,096 $ 23,096 $ 85,756 $ 85,756
Schedule of reclassification of accrued interest related to the early extinguishment of debt	However, the Company made the following reclassification of accrued interest related to the early extinguishment of debt on its Statements of Cash Flows for the year ended December 31, 2015: Year Ended December 31, 2015 (in thousands) As Previously Reported As Reclassified Cash flows used in financing activities $ (94,010 ) $ (87,618 ) Cash flows provided by operating activities $ 160,375 $ 153,983

Property Investments (Tables)

Property Investments (Tables)	12 Months Ended
	Dec. 31, 2017
Real Estate Investment Property, Net [Abstract]
Property Investment	The following table summarizes the Company’s investments at December 31, 2017. (Dollars in thousands) Number of Facilities Land Buildings, Improvements,and Lease Intangibles Personal Property Total Accumulated Depreciation Medical office/outpatient: Seattle, Washington 17 $ 24,560 $ 403,614 $ 378 $ 428,552 $ (52,457 ) Dallas, Texas 24 12,472 365,657 416 378,545 (128,557 ) Atlanta, Georgia 8 1,015 187,042 — 188,057 (1,203 ) Los Angeles, California 11 27,709 141,681 277 169,667 (71,808 ) Charlotte, North Carolina 16 4,200 163,603 95 167,898 (56,355 ) Nashville, Tennessee 5 3,143 149,859 278 153,280 (43,000 ) Richmond, Virginia 7 — 146,176 98 146,274 (32,299 ) Honolulu, Hawaii 3 8,327 132,847 159 141,333 (30,066 ) Denver, Colorado 6 4,086 122,689 271 127,046 (18,736 ) San Francisco, California 3 14,054 103,938 43 118,035 (12,223 ) Oklahoma City, Oklahoma 2 7,673 101,432 6 109,111 (10,890 ) Washington, D.C. 4 — 100,570 — 100,570 (15,826 ) Austin, Texas 4 12,756 85,961 105 98,822 (17,498 ) San Antonio, Texas 7 6,647 88,129 370 95,146 (34,514 ) Memphis, Tennessee 7 5,241 88,517 160 93,918 (31,675 ) Des Moines, Iowa 6 12,665 79,214 94 91,973 (18,263 ) Chicago, Illinois 3 5,859 79,295 200 85,354 (15,476 ) Indianapolis, Indiana 3 3,299 71,641 — 74,940 (18,742 ) Other (22 markets) 52 38,598 678,196 1,163 717,957 (206,844 ) 188 192,304 3,290,061 4,113 3,486,478 (816,432 ) Inpatient: Springfield, Missouri 1 1,989 109,304 — 111,293 (12,046 ) Dallas, Texas 1 4,442 92,990 — 97,432 (19,538 ) Erie, Pennsylvania 1 — 21,355 — 21,355 (15,152 ) Los Angeles, California 1 — 12,688 — 12,688 (7,606 ) Denver, Colorado 1 623 10,788 — 11,411 (1,781 ) 5 7,054 247,125 — 254,179 (56,123 ) Other: Des Moines, Iowa 1 — 40,354 5 40,359 (7,704 ) Johnson City, Tennessee 1 253 7,319 408 7,980 (2,798 ) Austin, Texas 1 1,480 3,872 2 5,354 (164 ) Fenton, Michigan 1 40 3,468 32 3,540 (2,738 ) Ovid, Michigan 1 62 3,188 49 3,299 (2,096 ) Fremont, Michigan 1 7 3,242 35 3,284 (2,565 ) St. Louis, Michigan 1 31 1,735 33 1,799 (1,341 ) Detroit, Michigan 1 52 1,096 34 1,182 (829 ) 8 1,925 64,274 598 66,797 (20,235 ) Land Held for Development — 20,123 — — 20,123 (239 ) Construction in Progress — — 5,458 — 5,458 — Corporate Property — — — 5,603 5,603 (4,401 ) — 20,123 5,458 5,603 31,184 (4,640 ) Total real estate investments 201 $ 221,406 $ 3,606,918 $ 10,314 $ 3,838,638 $ (897,430 )

Real Estate Leases (Tables)

Real Estate Leases (Tables)	12 Months Ended
	Dec. 31, 2017
Leases [Abstract]
Future minimum lease payments due to the Company under property operating agreements	Future minimum lease payments under the non-cancelable operating leases and guaranteed amounts payable to the Company under property operating agreements as of December 31, 2017 are as follows (in thousands): 2018 $ 330,526 2019 282,910 2020 236,454 2021 196,346 2022 168,183 2023 and thereafter 544,677 $ 1,759,096

Acquisitions, Dispositions an34

Acquisitions, Dispositions and Mortgage Repayments (Tables)	12 Months Ended
	Dec. 31, 2017
Acquisitions and Dispositions and Mortgage Repayments [Abstract]
Summary of acquisitions	The following table details the Company's acquisitions for the year ended December 31, 2016 : (Dollars in millions) Type (1) Date Purchase Price Mortgage (2) Cash (3) Real Other (4) Square (unaudited) Real estate acquisitions Seattle, Washington MOB 3/31/16 $ 38.3 $ — $ 37.7 $ 37.7 $ — 69,712 Seattle, Washington MOB 4/29/16 21.6 — 18.8 20.1 (1.3 ) 46,637 Los Angeles, California MOB 5/13/16 20.0 (13.2 ) 6.5 20.4 (0.7 ) 63,012 Seattle, Washington MOB 9/12/16 53.1 — 53.0 54.6 (1.6 ) 87,462 Washington, D.C. (5) MOB 9/26/16 45.2 — 45.1 43.7 1.4 103,783 Baltimore, Maryland (6) MOB 10/11/16 36.2 — 36.4 36.4 — 113,631 Seattle, Washington MOB 10/17/16 9.8 — 9.8 9.9 (0.1 ) 29,753 Seattle, Washington MOB 12/21/16 5.1 — 5.1 5.2 (0.1 ) 20,740 St. Paul, Minnesota MOB 12/21/16 12.6 — 12.5 11.3 1.2 48,281 $ 241.9 $ (13.2 ) $ 224.9 $ 239.3 $ (1.2 ) 583,011 ______ (1) MOB = medical office building (2) The mortgage notes payable assumed in the acquisitions do not reflect the fair value adjustments totaling $0.8 million recorded by the Company upon acquisition (included in Other). (3) Excludes prorations of revenue and expense due to/from seller at the time of the acquisition. (4) Includes other assets acquired, liabilities assumed, intangibles recognized at acquisition and fair value adjustments on debt assumed. (5) A director of the Company serves as the Chief Executive Officer of the Inova Health System. As part of this transaction, the Company assumed a ground lease and tenant leases with Loudon Hospital Center, an affiliate of Inova Health System. (6) Includes two properties. The following table details the Company's acquisitions for the year ended December 31, 2017 : (Dollars in millions) Type (1) Date Purchase Price Mortgage (2) Cash (3) Real Other (4) Square (Unaudited) Real estate acquisitions St. Paul, Minnesota MOB 3/6/17 $ 13.5 $ — $ 13.5 $ 13.3 $ 0.2 34,608 San Francisco, California MOB 6/12/17 26.8 — 26.8 26.8 — 75,649 Washington, D.C. MOB 6/13/17 24.0 (12.1 ) 12.5 24.8 (0.2 ) 62,379 Los Angeles, California MOB 7/31/17 16.3 — 16.7 16.9 (0.2 ) 42,780 Atlanta, Georgia MOB 11/1/17 25.5 — 25.5 26.3 (0.8 ) 76,944 Atlanta, Georgia MOB 11/1/17 30.3 — 30.7 30.7 — 74,024 Atlanta, Georgia (5) MOB 11/1/17 49.7 — 50.9 47.5 3.4 118,180 Atlanta, Georgia MOB 11/1/17 6.7 — 6.7 6.7 — 19,732 Seattle, Washington MOB 11/1/17 12.7 — 12.6 12.8 (0.2 ) 26,345 Atlanta, Georgia (5) MOB 12/13/17 25.8 (10.5 ) 15.3 22.0 3.8 59,427 Atlanta, Georgia MOB 12/13/17 15.4 (4.7 ) 10.8 15.7 (0.2 ) 40,171 Atlanta, Georgia (5) MOB 12/18/17 26.3 (11.8 ) 14.5 24.6 1.7 66,984 Atlanta, Georgia MOB 12/18/17 14.2 (6.7 ) 7.6 14.5 (0.2 ) 40,324 Chicago, Illinois MOB 12/18/17 28.7 — 27.7 28.5 (0.8 ) 99,526 Seattle, Washington MOB 12/18/17 8.8 — 8.8 9.0 (0.2 ) 32,828 Austin, Texas (6) MOB 12/21/17 2.5 — 2.5 2.5 — 7,972 $ 327.2 $ (45.8 ) $ 283.1 $ 322.6 $ 6.3 877,873 ______ (1) MOB = medical office building (2) The mortgage notes payable assumed in the acquisitions do not reflect the fair value adjustments totaling $0.6 million in aggregate recorded by the Company upon acquisition (included in Other). (3) Cash consideration excludes prorations of revenue and expense due to/from seller at the time of the acquisition. (4) Includes other assets acquired, liabilities assumed, intangibles recognized at acquisition and fair value adjustments on debt assumed. (5) The "Other" column includes the equity investment in limited liability companies that own two parking garages. (6) The Company acquired additional ownership interests in an existing building bringing the Company's ownership to 69.4% .
Summary of assets acquired and liabilities assumed	The following table summarizes the estimated relative fair values of the assets acquired and liabilities assumed in the real estate acquisitions for 2016 as of the acquisition date: Estimated Fair Value Estimated Useful Life (In millions) (In years) Building $ 216.8 20.0-35.0 Land 9.7 — Intangibles: At-market lease intangibles 12.8 2.7-10.3 Above-market lease intangibles 0.9 0.7-3.8 Below-market lease intangibles (0.4 ) 1.4-9.4 Above-market ground lease intangibles (1.6 ) 99.0 Below-market ground lease intangibles 2.0 36.8-99.0 Total intangibles 13.7 Mortgage notes payable assumed, including fair value adjustments (14.0 ) Other assets acquired 0.5 Accounts payable, accrued liabilities and other liabilities assumed (1.8 ) Total cash paid $ 224.9 The following table summarizes the estimated relative fair values of the assets acquired and liabilities assumed in the real estate acquisitions for 2017 as of the acquisition date: Estimated Fair Value Estimated Useful Life (In millions) (In years) Building $ 272.1 15.0-37.0 Land 11.7 — Land Improvements 1.6 5.0-12.0 Intangibles: At-market lease intangibles 37.2 2.1-12.6 Below-market lease intangibles (0.9 ) 8.5-15.0 Below-market ground lease intangibles 0.4 36.8-99.0 Total intangibles 36.7 Mortgage notes payable assumed, including fair value adjustments (46.4 ) Other assets acquired 0.4 Equity investment in joint ventures 8.7 Accounts payable, accrued liabilities and other liabilities assumed (1.7 ) Total cash paid $ 283.1
Summary of dispositions	2017 Real Estate Asset Dispositions The following table details the Company's dispositions for the year ended December 31, 2017 : (Dollars in millions) Type (1) Date Sales Price Closing Adjustments Net Net Real Other (3) Gain/ Square Unaudited ) Real estate dispositions Evansville, Indiana OTH 3/6/17 $ 6.4 $ — $ 6.4 $ 1.1 $ — $ 5.3 29,500 Columbus, Georgia (2) MOB 3/7/17 0.6 — 0.6 0.6 — — 12,000 Las Vegas, Nevada (2) MOB 3/30/17 5.5 (0.7 ) 4.8 2.2 0.3 2.3 18,147 Texas (3 properties) IRF 3/31/17 69.5 (1.6 ) 67.9 46.9 5.2 15.8 169,722 Chicago, Illinois (4) MOB 6/16/17 0.5 (0.1 ) 0.4 0.4 — — 5,100 San Antonio, Texas IRF 6/29/17 14.5 (0.2 ) 14.3 5.1 0.9 8.3 39,786 Roseburg, Oregon MOB 6/29/17 23.2 (0.6 ) 22.6 14.5 0.3 7.8 62,246 St. Louis, Missouri MOB 9/7/17 2.5 (0.1 ) 2.4 7.4 0.1 (5.1 ) 79,980 Total dispositions $ 122.7 $ (3.3 ) $ 119.4 $ 78.2 $ 6.8 $ 34.4 416,481 ______ (1) MOB = medical office building; IRF = inpatient rehabilitation facility; OTH = other (2) Previously classified as held for sale. (3) Includes straight-line rent receivables, leasing commissions and lease inducements. (4) The Company recorded an impairment of approximately $0.3 million in the first quarter of 2017 upon management's decision to sell. 2016 Real Estate Asset Dispositions The following table details the Company's dispositions for the year ended December 31, 2016 : (Dollars in millions) Type (1) Date Sales Price Closing Adjustments Net Net Real Other (2) Gain Square Unaudited ) Real estate dispositions Kansas City, Kansas MOB 10/14/16 $ 15.1 $ — $ 15.1 $ 7.2 $ 0.3 $ 7.6 70,908 Nashville, Tennessee MOB 10/28/16 8.8 (0.2 ) 8.6 6.3 0.2 2.1 45,274 Altoona, Pennsylvania IRF 12/20/16 21.5 (0.4 ) 21.1 12.4 0.6 8.1 64,032 Harrisburg, Pennsylvania IRF 12/20/16 24.2 (0.6 ) 23.6 8.2 0.4 15.0 79,836 Phoenix, Arizona IRF 12/20/16 22.3 — 22.3 13.5 1.4 7.4 51,903 Atlanta, Georgia MOB 12/22/16 2.8 (0.2 ) 2.6 1.8 — 0.8 8,749 Total dispositions $ 94.7 $ (1.4 ) $ 93.3 $ 49.4 $ 2.9 $ 41.0 320,702 ______ (1) MOB = medical office building; IRF = inpatient rehabilitation facility (2) Includes straight-line rent receivables, leasing commissions and lease inducements.

Held for Sale and Discontinue35

Held for Sale and Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2017
Discontinued Operations and Disposal Groups [Abstract]
Schedule of Disposal Groups, Including Discontinued Operations, Income Statement, Balance Sheet and Additional Disclosures	The table below reflects the assets and liabilities of the properties classified as held for sale and discontinued operations as of December 31, 2017 and 2016 . December 31, (Dollars in thousands) 2017 2016 Balance Sheet data Land $ 4,636 $ 1,362 Buildings, improvements and lease intangibles 63,654 4,410 Personal property 82 — 68,372 5,772 Accumulated depreciation (35,790 ) (2,977 ) Assets held for sale, net 32,582 2,795 Other assets, net (including receivables) 565 297 Assets of discontinued operations, net 565 297 Assets held for sale and discontinued operations, net $ 33,147 $ 3,092 Accounts payable and accrued liabilities $ 38 $ 22 Other liabilities 55 592 Liabilities of assets held for sale and discontinued operations $ 93 $ 614 The table below reflects the results of operations of the properties included in discontinued operations on the Company’s Consolidated Statements of Income for the years ended December 31, 2017 , 2016 and 2015 . Year Ended December 31, (Dollars in thousands, except per share data) 2017 2016 2015 Statements of Income data: Revenues (1) Rental income $ — $ — $ 752 Other operating — — — — — 752 Expenses (2) Property operating 19 71 58 Bad debt, net of recoveries (10 ) — (1 ) 9 71 57 Other Income (Expense) (3) Interest and other income, net — — 20 — — 20 Income (Loss) from Discontinued Operations (9 ) (71 ) 715 Impairments (4) — (121 ) (686 ) Gain on sales of real estate properties (5) 5 7 10,571 Income (Loss) from Discontinued Operations $ (4 ) $ (185 ) $ 10,600 Income (Loss) from Discontinued Operations per Common Share - Basic $ 0.00 $ 0.00 $ 0.11 Income (Loss) from Discontinued Operations per Common Share - Diluted $ 0.00 $ 0.00 $ 0.11 ______ (1) Total revenues for the year ended December 31, 2015 included $0.8 million related to properties sold. (2) Total expenses for the year ended December 31, 2016 included $0.1 million related to a property that is held for sale. Total expenses for the year ended December 31, 2015 included $0.1 million related to properties sold. (3) Other income (expense) for the year ended December 31, 2015 included income (expense) related to properties sold. (4) Impairments for the years ended December 31, 2016 and 2015 included $0.1 million and $0.7 million , respectively, related to one property sold. (5) Gain on sales of real estate properties for the year ended December 31, 2017 included a gain on the sale of one property sold in 2017. Gain on sales of real estate properties for the year ended December 31, 2016 included a gain on the sale of one property sold in 2015. Gains on the sales of real estate properties for the year ended December 31, 2015 included gains on the sale of one property

Other Assets (Tables)

Other Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Items included in other assets	Other assets consist primarily of straight-line rent receivables, prepaids, intangible assets, deferred financing costs and accounts receivable. Items included in "Other assets, net" on the Company’s Consolidated Balance Sheets as of December 31, 2017 and 2016 are detailed in the table below: December 31, (Dollars in millions) 2017 2016 Prepaid assets $ 65.2 $ 64.8 Equity investment in joint ventures 8.7 — Straight-line rent receivables 67.0 64.6 Above-market intangible assets, net 17.9 19.1 Additional long-lived assets, net 24.9 14.5 Ground lease modification, net 10.3 10.8 Accounts receivable 7.4 8.1 Allowance for uncollectible accounts (0.3 ) (0.1 ) Credit facility deferred financing costs 3.5 4.9 Goodwill 3.5 3.5 Customer relationship intangible assets, net 1.7 1.8 Other 3.2 3.7 $ 213.0 $ 195.7
Equity Method Investments	The Company's investment in and income (loss) recognized for the year ended December 31, 2017 related to its LLCs accounted for under the equity method are shown in the table below: (Dollars in millions) December 31, 2017 Net LLC investment, beginning of period $ — New investments during the period 8.7 Equity income (loss) recognized during the period — Net LLC investments, end of period $ 8.7

Intangible Assets and Liabili37

Intangible Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of finite lived intangible assets and liabilities	The Company’s intangible assets and liabilities as of December 31, 2017 and 2016 consisted of the following: Gross Balance at December 31, Accumulated Amortization at December 31, Weighted Avg. Remaining Life (Years) Balance Sheet Classification (Dollars in millions) 2017 2016 2017 2016 Goodwill $ 3.5 $ 3.5 $ — $ — N/A Other assets Credit facility deferred financing costs 5.4 5.4 1.9 0.5 2.6 Other assets Above-market lease intangibles 22.9 24.5 5.0 5.4 57.8 Other assets Customer relationship intangibles 2.6 2.6 0.9 0.8 25.6 Other assets Below-market lease intangibles (9.5 ) (8.8 ) (3.5 ) (3.2 ) 36.5 Other liabilities Deferred financing costs 9.3 9.4 1.8 4.0 4.5 Notes and Bonds Payable At-market lease intangibles 110.0 84.1 41.6 39.0 5.6 Real estate properties $ 144.2 $ 120.7 $ 47.7 $ 46.5 15.2
Schedule of expected net future amortization expense	The following table represents expected amortization over the next five years of the Company’s intangible assets and liabilities in place as of December 31, 2017 : (Dollars in millions) Future Amortization of Intangibles, net 2018 $ 19.8 2019 17.6 2020 12.0 2021 6.8 2022 5.8

Notes and Bonds Payable (Tables

Notes and Bonds Payable (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Instrument [Line Items]
Schedule of debt	December 31, Maturity Dates Contractual Interest Rates Principal Payments Interest Payments (Dollars in thousands) 2017 2016 Unsecured Credit Facility $ 189,000 $ 107,000 7/20 LIBOR + 1.00% At maturity Monthly Unsecured Term Loan due 2022 (1) 148,994 149,491 12/22 LIBOR + 1.10% At maturity Monthly Senior Notes due 2021 (1) — 397,147 1/21 5.75 % At maturity Semi-Annual Senior Notes due 2023 (1) 247,703 247,296 4/23 3.75 % At maturity Semi-Annual Senior Notes due 2025 (1) 248,044 247,819 5/25 3.88 % At maturity Semi-Annual Senior Notes due 2028 (1) 294,757 — 1/28 3.63 % At maturity Semi-Annual Mortgage notes payable (2) 155,382 115,617 12/18-5/40 3.31%-6.88% Monthly Monthly $ 1,283,880 $ 1,264,370 ______ (1) Balances are shown net of discounts and unamortized issuance costs. (2) Balances are shown net of discounts and unamortized issuance costs and including premiums.
Schedule of Mortgage Notes Payable	The following table details the Company’s mortgage notes payable, with related collateral. Original Balance Effective Interest Rate (23) Maturity Date Collateral (24) Principal and Interest Payments (22) Investment in Collateral at December 31, Balance at December 31, (Dollars in millions) 2017 2017 2016 Life Insurance Co. (1) 7.0 5.53 % 1/18 MOB Monthly/15-yr amort. $ — $ — $ 0.7 Commercial Bank (2) 1.8 5.55 % 10/30 OTH Monthly/27-yr amort. — — 1.3 Insurance Co. (3) 7.3 5.54 % 12/18 MOB Monthly/25-yr amort. 14.3 6.0 6.2 Commercial Bank (4) 9.5 5.07 % 3/19 MOB Monthly/5-yr amort. 13.9 9.3 9.5 Commercial Bank (5) 9.4 4.55 % 7/19 MOB Monthly/8-yr amort 27.8 9.2 9.3 Commercial Bank (6) 15.2 7.65 % 7/20 MOB (21) 20.2 12.7 12.7 Life Insurance Co. (7) 7.9 4.00 % 8/20 MOB Monthly/15-yr amort. 20.7 2.0 2.7 Life Insurance Co. (8) 7.3 5.25 % 8/20 MOB Monthly/27-yr amort. 17.9 6.5 6.7 Life Insurance Co. (9) 5.6 4.27 % 1/21 MOB Monthly/10-yr amort. 15.7 4.8 — Commercial Bank (10) 12.9 6.43 % 2/21 MOB Monthly/12-yr amort. 54.9 10.5 10.7 Life Insurance Co. (11) 11.0 3.85 % 11/22 MOB Monthly/7-yr amort. 22.0 10.4 — Life Insurance Co. (12) 12.3 3.85 % 8/23 MOB Monthly/7-yr amort. 24.6 11.5 — Financial Services (13) 12.4 4.27 % 10/23 MOB Monthly/10-yr amort. 24.7 12.2 — Life Insurance Co. (14) 13.3 4.13 % 1/24 MOB Monthly/10-yr amort. 21.1 13.3 13.6 Life Insurance Co. (15) 6.8 3.94 % 2/24 MOB Monthly/7-yr amort. 14.5 6.7 — Financial Services (16) 9.7 4.32 % 9/24 MOB Monthly/10-yr amort. 16.4 8.8 9.1 Commercial Bank 11.5 3.71 % 1/26 MOB Monthly/10-yr amort. 37.9 10.5 11.0 Commercial Bank (17) 15.0 5.25 % 4/27 MOB Monthly/20-yr amort. 33.4 9.6 10.4 Municipal Government (18) (19) 11.0 4.79 % (20) MOB Semi-Annual (20) 20.9 11.4 11.7 $ 400.9 $ 155.4 $ 115.6 ______ (1) The Company repaid this mortgage note in October 2017. The Company's unencumbered gross investment was $14.3 million at December 31, 2017. (2) The Company repaid this mortgage note in September 2017. The Company's unencumbered gross investment was $8.0 million at December 31, 2017. (3) The unamortized portion of the $0.6 million premium recorded on this note upon acquisition is included in the balance above. (4) The unamortized portion of the $0.2 million premium recorded on this note upon acquisition is included in the balance above. (5) The unamortized portion of the $0.3 million premium recorded on this note upon acquisition is included in the balance above. (6) The unaccreted portion of the $2.4 million discount recorded on this note upon acquisition is included in the balance above. (7) The unamortized portion of the $0.3 million premium recorded on this note upon acquisition is included in the balance above. (8) The unamortized portion of the $0.4 million premium recorded on this note upon acquisition is included in the balance above. (9) The unamortized portion of the $0.2 million premium recorded on this note upon acquisition is included in the balance above. (10) The unaccreted portion of the $1.0 million discount recorded on this note upon acquisition is included in the balance above. (11) The unaccreted portion of the $0.1 million discount recorded on this note upon acquisition is included in the balance above. (12) The unaccreted portion of the $0.2 million discount recorded on this note upon acquisition is included in the balance above. (13) The unamortized portion of the $0.4 million premium recorded upon acquisition is included in the balance above. (14) The unamortized portion of the $0.8 million premium recorded on this note upon acquisition is included in the balance above. (15) The unamortized portion of the $0.2 million premium recorded on this note upon acquisition is included in the balance above. (16) The unamortized portion of the $0.1 million premium recorded on this note upon acquisition is included in the balance above. (17) The unamortized portion of the $0.7 million premium recorded on this note upon acquisition is included in the balance above. (18) Balance consists of three notes secured by the same building. (19) The unamortized portion of the $1.0 million premium recorded on the three notes upon acquisition is included in the balance above. (20) These three mortgage notes payable are series municipal bonds that have maturity dates ranging from from May 2022 to May 2040. One of the four original notes payable was repaid upon maturity in May 2017. The remaining three require interest only payments and have future maturity dates but allow repayment after May 2020 without penalty. The Company intends on repaying all three notes payable at that time. (21) Payable in monthly installments of interest only for 24 months and then installments of principal and interest based on an 11 -year amortization with the final payment due at maturity. (22) Payable in monthly installments of principal and interest with the final payment due at maturity (unless otherwise noted). (23) The contractual interest rates for the 19 outstanding mortgage notes ranged from 3.3% to 6.9% as of December 31, 2017 . (24) MOB-Medical office building; OTH-Other.
Future contractual maturities of the Company's notes and bonds payable	Future maturities of the Company’s notes and bonds payable as of December 31, 2017 were as follows: (Dollars in thousands) Principal Maturities Net Accretion/ Amortization (1) Debt Issuance Costs (2) Notes and Bonds Payable % 2018 $ 10,605 $ (18 ) $ (1,051 ) 9,536 0.7 % 2019 22,711 (224 ) (1,044 ) 21,443 1.7 % 2020 211,803 (382 ) (1,039 ) 210,382 16.4 % 2021 17,321 (312 ) (1,025 ) 15,984 1.2 % 2022 162,692 (328 ) (1,037 ) 161,327 12.6 % 2023 and thereafter 868,784 (1,284 ) (2,292 ) 865,208 67.4 % $ 1,293,916 $ (2,548 ) $ (7,488 ) 1,283,880 100.0 % ______ (1) Includes discount accretion and premium amortization related to the Company’s Senior Notes due 2023, Senior Notes due 2025, Senior Notes due 2028 and 18 mortgage notes payable. (2) Excludes approximately $3.5 million in debt issuance costs related to the Company's Unsecured Credit Facility due 2020 included in other assets.
Senior Notes [Member] | Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Schedule of debt	The following table reconciles the balance of the Senior Notes due 2021 on the Company’s Consolidated Balance Sheets as of December 31, 2017 and 2016 : December 31, (Dollars in thousands) 2017 2016 Senior Notes due 2021 face value $ — $ 400,000 Unaccreted discount — (1,510 ) Issuance costs — (1,343 ) Senior Notes due 2021 carrying amount $ — $ 397,147
Senior Notes [Member] | Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Schedule of debt	The following table reconciles the balance of the Senior Notes due 2023 on the Company’s Consolidated Balance Sheets as of December 31, 2017 and 2016 : December 31, (Dollars in thousands) 2017 2016 Senior Notes due 2023 face value $ 250,000 $ 250,000 Unaccreted discount (1,178 ) (1,375 ) Issuance costs (1,119 ) (1,329 ) Senior Notes due 2023 carrying amount $ 247,703 $ 247,296
Senior Notes [Member] | Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Schedule of debt	The following table reconciles the balance of the Senior Notes due 2025 on the Company’s Consolidated Balance Sheets as of December 31, 2017 and 2016 : December 31, (Dollars in thousands) 2017 2016 Senior Notes due 2025 face value $ 250,000 $ 250,000 Unaccreted discount (160 ) (178 ) Issuance costs (1,796 ) (2,003 ) Senior Notes due 2025 carrying amount $ 248,044 $ 247,819
Senior Notes [Member] | Senior Notes due 2028 [Member]
Debt Instrument [Line Items]
Schedule of debt	The following table reconciles the balance of the Senior Notes due 2028 on the Company’s Consolidated Balance Sheets as of December 31, 2017 : (Dollars in thousands) December 31, 2017 Senior Notes due 2028 face value $ 300,000 Unaccreted discount (2,529 ) Issuance costs $ (2,714 ) Senior Notes due 2028 carrying amount $ 294,757
Mortgage Notes [Member] | Mortgage notes payable [Member]
Debt Instrument [Line Items]
Schedule of debt	The following table reconciles the Company’s aggregate mortgage notes principal balance with the Company’s Consolidated Balance Sheets as of December 31, 2017 and 2016 . For the years ended December 31, 2017 , 2016 and 2015 , the Company amortized approximately $0.3 million , $0.3 million and $0.8 million of the discount and $0.7 million , $0.9 million , and $1.0 million of the premium. For the years ended December 31, 2017, 2016 and 2015, the Company also amortized approximately $0.1 million , $0.2 million , and $0.2 million of the debt issuance costs, respectively, on the mortgage notes payable which is included in interest expense on the Company’s Consolidated Statements of Income. December 31, (Dollars in thousands) 2017 2016 Mortgage notes payable principal balance $ 154,916 $ 114,934 Unamortized premium 2,651 2,569 Unaccreted discount (1,332 ) (1,450 ) Issuance costs (853 ) (436 ) Mortgage notes payable carrying amount $ 155,382 $ 115,617

Derivative Financial Instrume39

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Cash Flow Hedges Included in Accumulated Other Comprehensive Income (Loss)	During the year ended December 31, 2017 , the Company entered into two outstanding interest rate derivatives that were designated as cash flow hedges of interest rate risk: Interest Rate Derivative Number of Instruments Notional (in millions) Interest rate swaps 2 $25.0
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value	The table below presents the fair value of the Company's derivative financial instruments, as well as, their classification on the Consolidated Balance Sheets as of December 31, 2017. Liability Derivatives As of December 31, 2017 (Dollars in thousands) Balance Sheet Location Fair Value Derivatives designated as hedging instruments Interest rate swaps Other liabilities $ 67 Total derivatives designated as hedging instruments $ 67
Schedule of Derivative Instruments, Effect on Other Comprehensive Income (Loss)	The table below presents the effect of cash flow hedge accounting on Accumulated Other Comprehensive Income (Loss) as of December 31, 2017 related to the Company's outstanding interest rate swaps. Amount of Loss Recognized in OCI on Derivative Amount of Loss Reclassified from OCI into Income (Dollars in thousands) 2017 2017 2016 Interest rate products $ 74 Interest expense $ 7 $ — Settled interest rate swaps — Interest expense 169 168 $ 74 Total interest expense $ 176 $ 168

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Reconciliation of the beginning and ending common stock outstanding	The Company had no preferred shares outstanding and had common shares outstanding for the three years ended December 31, 2017 as follows: Year Ended December 31, 2017 2016 2015 Balance, beginning of year 116,416,900 101,517,009 98,828,098 Issuance of common stock 8,395,607 14,063,100 2,493,171 Non-vested stock-based awards, net of withheld shares and forfeitures 319,086 836,791 195,740 Balance, end of year 125,131,593 116,416,900 101,517,009
Schedule of sale of stock under market equity offering Program	The following table details the shares sold under this program. Shares Sold Sales Price Per Share Net Proceeds (in millions) 2017 — NA $ — 2016 4,795,601 $28.31 - $33.66 $ 144.6 2015 2,434,239 $25.00 - $29.15 $ 65.8
Reconciliation of beginning and ending balances of accumulated other comprehensive income	The following table represents the changes in accumulated other comprehensive loss during the year ended December 31, 2017 : (Dollars in thousands) Interest Rate Swaps Beginning balance $ (1,401 ) Other comprehensive loss before reclassifications 176 Amounts reclassified from accumulated other comprehensive income (loss) (74 ) Net current-period other comprehensive income 102 Ending balance $ (1,299 )
Reclassifications out of accumulated other comprehensive income	The following table represents the details regarding the reclassifications from Accumulated other comprehensive income (loss) during the year ended December 31, 2017 : Details about accumulated other comprehensive income (loss) components Amount reclassified from accumulated other comprehensive income (loss) Affected line item in the statement where net income is presented (Dollars in thousands) Amounts reclassified from accumulated other comprehensive income (loss) related to settled interest rate swaps $ 169 Interest Expense Amounts reclassified from accumulated other comprehensive income (loss) related to current interest rate swaps 7 Interest Expense $ 176

Benefit Plans (Tables)

Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Net periodic benefit cost for both the Executive Retirement Plan and the Outside Director Plan	Net periodic benefit cost for the Executive Retirement Plan for the three years in the period ended December 31, 2017 is comprised of the following: Year Ended December 31, (Dollars in thousands) 2017 2016 2015 Service cost $ — $ — $ 29 Interest cost — — 225 Amortization of prior service cost (benefit) — — (198 ) Amortization of net gain — — 343 — — 399 Net loss recognized in Accumulated other comprehensive income (loss) — — — Total recognized in net periodic benefit gain and Accumulated other comprehensive income (1) $ — $ — $ 399 _____ (1) 2015 is a partial year due to the termination of the Executive Retirement Plan during the year.

Stock and Other Incentive Pla42

Stock and Other Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Unrecognized Compensation Cost, Nonvested Awards	The following table represents expected amortization of the Company's non-vested shares issued: (Dollars in millions) Future Amortization of Non-Vested Shares 2018 $ 9.4 2019 7.0 2020 6.7 2021 5.7 2022 3.2 2023 and thereafter 3.6 Total $ 35.6
Summary of the activity under the Incentive Plan the previous directors' plan	A summary of the activity under the 2015 Incentive Plan and related information for the three years in the period ended December 31, 2017 follows: Year Ended December 31, (Dollars in thousands, except per share data) 2017 2016 2015 Stock-based awards, beginning of year 1,786,497 1,092,262 1,057,732 Granted 413,489 885,219 251,789 Vested (292,341 ) (190,984 ) (210,955 ) Forfeited — — (6,304 ) Stock-based awards, end of year 1,907,645 1,786,497 1,092,262 Weighted-average grant date fair value of: Stock-based awards, beginning of year $ 27.18 $ 24.72 $ 24.01 Stock-based awards granted during the year $ 32.05 $ 29.60 $ 27.70 Stock-based awards vested during the year $ 25.88 $ 24.34 $ 25.05 Stock-based awards forfeited during the year $ — $ — $ 24.80 Stock-based awards, end of year $ 28.44 $ 27.18 $ 24.72 Grant date fair value of shares granted during the year $ 13,254 $ 26,204 $ 6,975
Summary of the Employee Stock Purchase Plan activity	A summary of the Employee Stock Purchase Plan activity and related information for the three years in the period ended December 31, 2017 is as follows: Year Ended December 31, (Dollars in thousands, except per share data) 2017 2016 2015 Options outstanding, beginning of year 316,321 340,958 393,902 Granted 206,824 198,450 197,640 Exercised (32,076 ) (57,924 ) (44,462 ) Forfeited (40,659 ) (22,081 ) (47,176 ) Expired (132,310 ) (143,082 ) (158,946 ) Options outstanding and exercisable, end of year 318,100 316,321 340,958 Weighted-average exercise price of: Options outstanding, beginning of year $ 23.69 $ 20.70 $ 19.17 Options granted during the year $ 25.77 $ 24.07 $ 23.22 Options exercised during the year $ 24.31 $ 21.40 $ 19.41 Options forfeited during the year $ 25.01 $ 23.16 $ 19.90 Options expired during the year $ 23.22 $ 18.11 $ 20.41 Options outstanding, end of year $ 25.00 $ 23.69 $ 20.70 Weighted-average fair value of options granted during the year (calculated as of the grant date) $ 6.31 $ 5.37 $ 5.39 Intrinsic value of options exercised during the year $ 271 $ 634 $ 381 Intrinsic value of options outstanding and exercisable (calculated as of December 31) $ 2,683 $ 2,098 $ 2,597 Exercise prices of options outstanding (calculated as of December 31) $ 25.00 $ 23.69 $ 20.70 Weighted-average contractual life of outstanding options (calculated as of December 31, in years) 0.8 0.8 0.8
Fair value of options issued based on weighted-average assumptions	2017 2016 2015 Risk-free interest rates 1.20 % 1.06 % 0.67 % Expected dividend yields 3.70 % 4.64 % 4.79 % Expected life (in years) 1.45 1.42 1.38 Expected volatility 20.4 % 17.6 % 21.0 % Expected forfeiture rates 85 % 85 % 80 %

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings per share	The table below sets forth the computation of basic and diluted earnings per common share for the three years in the period ended December 31, 2017 . Year Ended December 31, (Dollars in thousands, except per share data) 2017 2016 2015 Weighted Average Common Shares Weighted average Common Shares outstanding 119,739,216 109,861,580 100,280,059 Non-vested shares (1,813,058 ) (1,289,478 ) (1,108,707 ) Weighted average Common Shares - Basic 117,926,158 108,572,102 99,171,352 Weighted average Common Shares - Basic 117,926,158 108,572,102 99,171,352 Dilutive effect of non-vested shares — 709,559 623,212 Dilutive effect of employee stock purchase plan 91,007 105,336 85,738 Weighted average Common Shares - Diluted 118,017,165 109,386,997 99,880,302 Net Income Income from continuing operations $ 23,096 $ 85,756 $ 58,836 Dividends paid on nonvested share-based awards (2,149 ) — — Income from continuing operations applicable to common stockholders 20,947 85,756 58,836 Discontinued operations (4 ) (185 ) 10,600 Net income applicable to common stockholders $ 20,943 $ 85,571 $ 69,436 Basic Earnings Per Common Share Income from continuing operations $ 0.18 $ 0.79 $ 0.59 Income from discontinued operations 0.00 0.00 0.11 Net income $ 0.18 $ 0.79 $ 0.70 Diluted Earnings Per Common Share Income from continuing operations $ 0.18 $ 0.78 $ 0.59 Income from discontinued operations 0.00 0.00 0.11 Net income $ 0.18 $ 0.78 $ 0.70

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of construction activity	The table below details the Company’s construction activity as of December 31, 2017 . The information included in the table below represents management’s estimates and expectations at December 31, 2017 , which are subject to change. The Company’s disclosures regarding certain projections or estimates of completion dates may not reflect actual results. December 31, 2017 (Dollars in thousands) Number of Properties Estimated Completion Date Construction in Progress Balance Total Funded During the Year Total Amount Funded Estimated Remaining Fundings (unaudited) Estimated Total Investment (unaudited) Approximate Square Feet (unaudited) Construction Activity Charlotte, NC 1 Q1 2019 $ 3,487 $ 3,264 $ 3,487 8,513 $ 12,000 204,000 Seattle, WA 1 Q2 2019 1,971 1,809 2,272 61,848 64,120 151,000 Total $ 5,458 $ 5,073 $ 5,759 $ 70,361 $ 76,120 355,000
Minimum lease payments for its operating leases	The Company’s future minimum lease payments for its corporate office lease and 61 ground leases, excluding leases that the Company has prepaid and leases in which an operator pays or fully reimburses the Company, as of December 31, 2017 were as follows (in thousands): 2018 $ 5,341 2019 5,420 2020 5,459 2021 5,488 2022 5,516 2023 and thereafter 283,056 $ 310,280

Other Data (Tables)

Other Data (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Taxable Income	The following table reconciles the Company’s consolidated net income attributable to common stockholders to taxable income for the three years ended December 31, 2017 : Year Ended December 31, (Dollars in thousands) 2017 2016 2015 Net income $ 23,092 $ 85,571 $ 69,436 Reconciling items to taxable income: Depreciation and amortization 46,426 38,260 30,457 Gain or loss on disposition of depreciable assets 1,570 (32,103 ) 1,659 Impairments — 121 687 Straight-line rent (4,551 ) (7,101 ) (8,833 ) Receivable allowances 1,680 2,067 571 Stock-based compensation 1,855 1,301 7,518 Other 6,552 2,236 4,304 53,532 4,781 36,363 Taxable income (1) $ 76,624 $ 90,352 $ 105,799 Dividends paid $ 142,327 $ 131,759 $ 120,266 ______ (1) Before REIT dividend paid deduction
Characterization of distributions on common stock	For the three years ended December 31, 2017 , there were no preferred shares outstanding. As such, no dividends were distributed related to preferred shares for those periods. 2017 2016 2015 Per Share % Per Share % Per Share % Common stock: Ordinary income $ 0.42 34.5 % $ 0.78 65.0 % $ 0.61 51.0 % Return of capital 0.50 42.0 % 0.35 29.5 % 0.08 6.7 % Unrecaptured section 1250 gain 0.28 23.5 % 0.07 5.5 % 0.51 42.3 % Common stock distributions $ 1.20 100.0 % $ 1.20 100.0 % $ 1.20 100.0 %
State Income Taxes	State income tax expense and state income tax payments for the three years ended December 31, 2017 are detailed in the table below: Year Ended December 31, (Dollars in thousands) 2017 2016 2015 State income tax expense: Texas gross margins tax (1) $ 608 $ 562 $ 528 Other — 2 37 Total state income tax expense $ 608 $ 564 $ 565 State income tax payments, net of refunds and collections $ 555 $ 544 $ 758 ______ (1) In the table above, income tax expense for 2015 includes approximately $50 thousand that was recorded to the gain on sale of real estate properties sold, which is included in discontinued operations rather than general and administrative expenses on the Company’s Consolidated Statements of Income.

Fair Value of Financial Instr46

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair value and carrying values for notes and bonds payable, mortgage notes receivable and notes receivable	The table below details the fair value and carrying values for notes and bonds payable as of December 31, 2017 and 2016 . December 31, 2017 December 31, 2016 (Dollars in millions) Carrying Value Fair Value Carrying Value Fair Value Notes and bonds payable (1) $ 1,283.9 $ 1,269.7 $ 1,264.4 $ 1,265.1 ______ (1) Level 2 – model-derived valuations in which significant inputs and significant value drivers are observable in active markets.

Selected Quarterly Financial 47

Selected Quarterly Financial Data (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Selected Quarterly Financial Information [Abstract]
Summary of quarterly financial information	Quarterly financial information for the year ended December 31, 2017 is summarized below. Quarter Ended (Dollars in thousands, except per share data) March 31 (1) June 30 (2) September 30 (3) December 31 (4) 2017 Revenues from continuing operations $ 104,569 $ 105,245 $ 106,953 $ 107,731 Income (loss) from continuing operations 31,858 25,224 3,165 (37,151 ) Income (loss) from discontinued operations (13 ) — 8 — Net income (loss) attributable to common stockholders $ 31,845 $ 25,224 $ 3,173 $ (37,151 ) Net income attributable to common stockholders per share: Basic earnings per common share $ 0.28 $ 0.22 $ 0.02 $ (0.31 ) Diluted earnings per common share $ 0.28 $ 0.22 $ 0.02 $ (0.31 ) ______ (1) The increases in net income and amounts per share for the first quarter of 2017 are primarily attributable to gains of $23.4 million on the sale of six properties. (2) The increases in net income and amounts per share for the second quarter of 2017 are primarily attributable to gains of $16.1 million on the sale of three properties. (3) The decreases in net income and amounts per share for the third quarter of 2017 are primarily attributable to impairment charges of $5.1 million . (4) The decreases in net income and amounts per share for the fourth quarter of 2017 are primarily attributable to a loss on the extinguishment of debt of $45.0 million . Quarterly financial information for the year ended December 31, 2016 is summarized below. Quarter Ended (Dollars in thousands, except per share data) March 31 June 30 September 30 December 31 (1) 2016 Revenues from continuing operations $ 100,021 $ 102,642 $ 103,659 $ 105,309 Income from continuing operations 9,163 12,157 11,857 52,580 Loss from discontinued operations (7 ) (12 ) (23 ) (143 ) Net income attributable to common stockholders $ 9,156 $ 12,145 $ 11,834 $ 52,437 Net income attributable to common stockholders per share: Basic earnings per common share $ 0.09 $ 0.12 $ 0.10 $ 0.46 Diluted earnings per common share $ 0.09 $ 0.12 $ 0.10 $ 0.45 ______ (1) The increases in net income and amounts per share for the fourth quarter of 2016 are primarily attributable to gains of $41.0 million on the sale of six properties.

Summary of Significant Accoun48

Summary of Significant Accounting Policies - Cash and cash equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Cash and cash equivalents	$ 6,215	$ 5,409
Restricted cash	0	49,098
Total cash, cash equivalents and restricted cash	$ 6,215	$ 54,507	$ 4,102	$ 3,519

Summary of Significant Accoun49

Summary of Significant Accounting Policies - Useful lives of real estate assets and liabilities (Details)	12 Months Ended
	Dec. 31, 2017
Land improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Asset estimated useful life	5 years
Land improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Asset estimated useful life	39 years
Building and improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Asset estimated useful life	3 years 3 months 18 days
Building and improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Asset estimated useful life	39 years
Lease intangibles (including ground lease intangibles) [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Asset estimated useful life	2 years 1 month 6 days
Intangible asset useful life	2 years 1 month 6 days
Lease intangibles (including ground lease intangibles) [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Asset estimated useful life	99 years 6 days
Intangible asset useful life	99 years
Personal property [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Asset estimated useful life	2 years 9 months 18 days
Personal property [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Asset estimated useful life	20 years

Summary of Significant Accoun50

Summary of Significant Accounting Policies - Components of rental income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Property operating income	$ 363,907	$ 336,409	$ 306,550
Single-tenant net lease	52,873	63,871	67,238
Straight-line rent	6,072	7,201	9,545
Rental income	$ 422,852	$ 407,481	$ 383,333

Summary of Significant Accoun51

Summary of Significant Accounting Policies - Components of other operating income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Operating Income [Abstract]
Property lease guaranty revenue	$ 726	$ 3,058	$ 3,890
Interest income	361	473	579
Management fee income	276	369	370
Other	284	249	208
Other operating	$ 1,647	$ 4,149	$ 5,047

Summary of Significant Accoun52

Summary of Significant Accounting Policies - Reclassifications (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
General and administrative	$ 32,992	$ 31,309	$ 24,716
Acquisition and pursuit costs	2,180	4,496	2,209
Total		35,805	26,925
Depreciation		0	0
Amortization		0	0
Depreciation and amortization	142,472	127,690	116,614
Total		127,690	116,614
Cash flows used in financing activities	31,390	136,957	(87,618)
Cash flows provided by operating activities	$ 179,766	151,272	153,983
As Previously Reported
Property, Plant and Equipment [Line Items]
General and administrative		35,805	26,925
Acquisition and pursuit costs		0	0
Total		35,805	26,925
Depreciation		116,483	106,530
Amortization		11,207	10,084
Depreciation and amortization		0	0
Total		$ 127,690	116,614
Cash flows used in financing activities			(94,010)
Cash flows provided by operating activities			$ 160,375

Summary of Significant Accoun53

Summary of Significant Accounting Policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2017USD ($)ft²land_parcelreporting_unitstatepropertyswap_agreement	Dec. 31, 2016USD ($)land_parcelpropertyswap_agreement	Dec. 31, 2015USD ($)propertyswap_agreement
Business Overview [Abstract]
Gross investment, amount, total	$ 3,800,000,000
Real estate properties and mortgages | property	201
Number of owned real estate properties | property	201
Number of states that the Company owns real estate in | state	27
Square footage of owned real estate properties | ft²	14,600,000
Approximate square feet for which Nationwide property management services provided by company | ft²	11,500,000
Segment Reporting [Abstract]
Number of Reporting Units | reporting_unit	1
Real Estate Properties [Abstract]
Total real estate properties	$ 3,838,638,000	$ 3,628,221,000
Depreciation	$ 129,400,000	$ 116,500,000	$ 106,500,000
Maximum period up to which interest capitalize on properties in stabilization	1 year
Land Held for Development [Abstract]
Number of land parcels held for development | land_parcel	6	6
Land held for development	$ 20,100,000	$ 20,100,000
Fair Value Measurements [Abstract]
Impairment of real estate	5,385,000		3,639,000
Goodwill and Intangible Assets [Abstract]
Goodwill impairment loss	0	0
Goodwill	$ 3,487,000	3,487,000
Incentive Plans [Abstract]
Discount on market price on the date of grant	85.00%
Discount on market price on the date of exercise	85.00%
Expiration date	27 months
General and administrative	$ 32,992,000	$ 31,309,000	$ 24,716,000
Accumulated Other Comprehensive Income (Loss) [Abstract]
Number of forward starting swaps settled | swap_agreement	4	4	4
Revenue Recognition [Abstract]
Deferred revenue	$ 36,000,000	$ 32,400,000
Deferred revenue, tenant reimbursements	20,100,000	20,600,000
Rental Income [Abstract]
Operating expense recoveries included in income from continuing operations	$ 73,400,000	$ 66,000,000	$ 58,900,000
Additional rental income, net of reserves included in income from continuing operations			$ 700,000
Other Operating Income [Abstract]
Number of owned real estate properties to which property operating agreements between company and sponsoring health system is applicable | property	1	2	5
Federal Income Taxes [Abstract]
Percentage of distribution of taxable income for qualify as REIT	90.00%
At Market Lease Intangibles [Member]
Real Estate Properties [Abstract]
Elimination of real estate lease intangibles against accumulated depreciation	$ 10,200,000	$ 6,700,000
Employee Stock Purchase Plan [Member]
Incentive Plans [Abstract]
General and administrative	200,000	200,000	$ 200,000
Tenant and Capital Improvements [Member]
Real Estate Properties [Abstract]
Fully depreciated tenant and capital improvements eliminated against accumulated depreciation	2,600,000	100,000
Forward Starting Interest Rate Swap [Member]
Derivative Instrument Detail [Abstract]
Accumulated other comprehensive income (loss), net of tax	$ 1,300,000	$ 1,400,000
Customer Concentration Risk [Member] | Revenue [Member]
Risks and Uncertainties [Abstract]
Concentration risk (percent)	9.70%	9.80%	9.80%
Medical Office Building [Member]
Business Overview [Abstract]
Square footage of owned real estate properties | ft²	355,000
Medical Office Building [Member] | Level 1 [Member]
Fair Value Measurements [Abstract]
Impairment of real estate	$ 5,100,000
Real estate dispositions [Member] | Level 1 [Member]
Fair Value Measurements [Abstract]
Impairment of real estate	$ 300,000

Summary of Significant Accoun54

Summary of Significant Accounting Policies - Impact of new accounting pronouncements (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Rental income									$ 422,852	$ 407,481	$ 383,333
Other operating									1,647	4,149	5,047
Revenues	$ 107,731	$ 106,953	$ 105,245	$ 104,569	$ 105,309	$ 103,659	$ 102,642	$ 100,021	424,499	411,630	388,471
Interest and other income, net									896	375	389
Income from continuing operations	$ (37,151)	$ 3,165	$ 25,224	$ 31,858	$ 52,580	$ 11,857	$ 12,157	$ 9,163	23,096	85,756	$ 58,836
As Reclassified
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Rental income									416,727	401,989
Other operating									8,011	9,966
Revenues									424,738	411,955
Interest and other income, net									658	50
Income from continuing operations									$ 23,096	$ 85,756

Property Investments (Details)

Property Investments (Details) $ in Thousands	Dec. 31, 2017USD ($)property	Dec. 31, 2016USD ($)
Summary of Company's investment
Number of facilities | property	201
Number of real estate investments | property	201
Land	$ 221,406
Buildings, Improvements,and Lease Intangibles	3,601,460	$ 3,386,480
Buildings, Improvements, and Lease Intangibles, including Construction in Progress	3,606,918
Personal Property	10,314	10,291
Total real estate properties	3,838,638	3,628,221
Accumulated Depreciation	(897,430)	$ (840,839)
Total real estate investments	3,838,638
Wholly Owned Properties [Member]
Summary of Company's investment
Accumulated Depreciation	$ (897,430)
Land Held for Development and Corporate Property [Member]
Summary of Company's investment
Number of facilities | property	0
Land	$ 20,123
Buildings, Improvements,and Lease Intangibles	5,458
Personal Property	5,603
Total real estate properties	31,184
Accumulated Depreciation	$ (4,640)
Land Held for Development [Member]
Summary of Company's investment
Number of facilities | property	0
Land	$ 20,123
Buildings, Improvements,and Lease Intangibles	0
Personal Property	0
Total real estate properties	20,123
Accumulated Depreciation	(239)
Construction in Progress [Member]
Summary of Company's investment
Buildings, Improvements,and Lease Intangibles	5,458
Total real estate properties	$ 5,458
Corporate Property [Member]
Summary of Company's investment
Number of facilities | property	0
Land	$ 0
Buildings, Improvements,and Lease Intangibles	0
Personal Property	5,603
Total real estate properties	5,603
Accumulated Depreciation	$ (4,401)
Medical office/outpatient [Member]
Summary of Company's investment
Number of facilities | property	188
Land	$ 192,304
Buildings, Improvements,and Lease Intangibles	3,290,061
Personal Property	4,113
Total real estate properties	3,486,478
Accumulated Depreciation	$ (816,432)
Medical office/outpatient [Member] | Colorado [Member]
Summary of Company's investment
Number of facilities | property	6
Land	$ 4,086
Buildings, Improvements,and Lease Intangibles	122,689
Personal Property	271
Total real estate properties	127,046
Accumulated Depreciation	$ (18,736)
Medical office/outpatient [Member] | DISTRICT OF COLUMBIA
Summary of Company's investment
Number of facilities | property	4
Land	$ 0
Buildings, Improvements,and Lease Intangibles	100,570
Personal Property	0
Total real estate properties	100,570
Accumulated Depreciation	$ (15,826)
Medical office/outpatient [Member] | Georgia [Member]
Summary of Company's investment
Number of facilities | property	8
Land	$ 1,015
Buildings, Improvements,and Lease Intangibles	187,042
Personal Property	0
Total real estate properties	188,057
Accumulated Depreciation	$ (1,203)
Medical office/outpatient [Member] | Austin, Texas [Member]
Summary of Company's investment
Number of facilities | property	4
Land	$ 12,756
Buildings, Improvements,and Lease Intangibles	85,961
Personal Property	105
Total real estate properties	98,822
Accumulated Depreciation	$ (17,498)
Medical office/outpatient [Member] | Hawaii [Member]
Summary of Company's investment
Number of facilities | property	3
Land	$ 8,327
Buildings, Improvements,and Lease Intangibles	132,847
Personal Property	159
Total real estate properties	141,333
Accumulated Depreciation	$ (30,066)
Medical office/outpatient [Member] | Illinois [Member]
Summary of Company's investment
Number of facilities | property	3
Land	$ 5,859
Buildings, Improvements,and Lease Intangibles	79,295
Personal Property	200
Total real estate properties	85,354
Accumulated Depreciation	$ (15,476)
Medical office/outpatient [Member] | Dallas, Texas [Member]
Summary of Company's investment
Number of facilities | property	24
Land	$ 12,472
Buildings, Improvements,and Lease Intangibles	365,657
Personal Property	416
Total real estate properties	378,545
Accumulated Depreciation	$ (128,557)
Medical office/outpatient [Member] | Indiana [Member]
Summary of Company's investment
Number of facilities | property	3
Land	$ 3,299
Buildings, Improvements,and Lease Intangibles	71,641
Personal Property	0
Total real estate properties	74,940
Accumulated Depreciation	$ (18,742)
Medical office/outpatient [Member] | Memphis, Tennessee [Member]
Summary of Company's investment
Number of facilities | property	7
Land	$ 5,241
Buildings, Improvements,and Lease Intangibles	88,517
Personal Property	160
Total real estate properties	93,918
Accumulated Depreciation	$ (31,675)
Medical office/outpatient [Member] | Nashville, Tennessee [Member]
Summary of Company's investment
Number of facilities | property	5
Land	$ 3,143
Buildings, Improvements,and Lease Intangibles	149,859
Personal Property	278
Total real estate properties	153,280
Accumulated Depreciation	$ (43,000)
Medical office/outpatient [Member] | Iowa [Member]
Summary of Company's investment
Number of facilities | property	6
Land	$ 12,665
Buildings, Improvements,and Lease Intangibles	79,214
Personal Property	94
Total real estate properties	91,973
Accumulated Depreciation	$ (18,263)
Medical office/outpatient [Member] | North Carolina [Member]
Summary of Company's investment
Number of facilities | property	16
Land	$ 4,200
Buildings, Improvements,and Lease Intangibles	163,603
Personal Property	95
Total real estate properties	167,898
Accumulated Depreciation	$ (56,355)
Medical office/outpatient [Member] | Oklahoma [Member]
Summary of Company's investment
Number of facilities | property	2
Land	$ 7,673
Buildings, Improvements,and Lease Intangibles	101,432
Personal Property	6
Total real estate properties	109,111
Accumulated Depreciation	$ (10,890)
Medical office/outpatient [Member] | Los Angeles, California [Member]
Summary of Company's investment
Number of facilities | property	11
Land	$ 27,709
Buildings, Improvements,and Lease Intangibles	141,681
Personal Property	277
Total real estate properties	169,667
Accumulated Depreciation	$ (71,808)
Medical office/outpatient [Member] | Virginia [Member]
Summary of Company's investment
Number of facilities | property	7
Land	$ 0
Buildings, Improvements,and Lease Intangibles	146,176
Personal Property	98
Total real estate properties	146,274
Accumulated Depreciation	$ (32,299)
Medical office/outpatient [Member] | San Antonio, Texas [Member]
Summary of Company's investment
Number of facilities | property	7
Land	$ 6,647
Buildings, Improvements,and Lease Intangibles	88,129
Personal Property	370
Total real estate properties	95,146
Accumulated Depreciation	$ (34,514)
Medical office/outpatient [Member] | San Francisco, California [Member]
Summary of Company's investment
Number of facilities | property	3
Land	$ 14,054
Buildings, Improvements,and Lease Intangibles	103,938
Personal Property	43
Total real estate properties	118,035
Accumulated Depreciation	$ (12,223)
Medical office/outpatient [Member] | Washington [Member]
Summary of Company's investment
Number of facilities | property	17
Land	$ 24,560
Buildings, Improvements,and Lease Intangibles	403,614
Personal Property	378
Total real estate properties	428,552
Accumulated Depreciation	$ (52,457)
Medical office/outpatient [Member] | Other (22 MSAs) [Member]
Summary of Company's investment
Number of facilities | property	52
Land	$ 38,598
Buildings, Improvements,and Lease Intangibles	678,196
Personal Property	1,163
Total real estate properties	717,957
Accumulated Depreciation	$ (206,844)
Inpatient [Member]
Summary of Company's investment
Number of facilities | property	5
Land	$ 7,054
Buildings, Improvements,and Lease Intangibles	247,125
Personal Property	0
Total real estate properties	254,179
Accumulated Depreciation	$ (56,123)
Inpatient [Member] | Colorado [Member]
Summary of Company's investment
Number of facilities | property	1
Land	$ 623
Buildings, Improvements,and Lease Intangibles	10,788
Personal Property	0
Total real estate properties	11,411
Accumulated Depreciation	$ (1,781)
Inpatient [Member] | Dallas, Texas [Member]
Summary of Company's investment
Number of facilities | property	1
Land	$ 4,442
Buildings, Improvements,and Lease Intangibles	92,990
Personal Property	0
Total real estate properties	97,432
Accumulated Depreciation	$ (19,538)
Inpatient [Member] | Missouri [Member]
Summary of Company's investment
Number of facilities | property	1
Land	$ 1,989
Buildings, Improvements,and Lease Intangibles	109,304
Personal Property	0
Total real estate properties	111,293
Accumulated Depreciation	$ (12,046)
Inpatient [Member] | Los Angeles, California [Member]
Summary of Company's investment
Number of facilities | property	1
Land	$ 0
Buildings, Improvements,and Lease Intangibles	12,688
Personal Property	0
Total real estate properties	12,688
Accumulated Depreciation	$ (7,606)
Inpatient [Member] | Pennsylvania [Member]
Summary of Company's investment
Number of facilities | property	1
Land	$ 0
Buildings, Improvements,and Lease Intangibles	21,355
Personal Property	0
Total real estate properties	21,355
Accumulated Depreciation	$ (15,152)
Other [Member]
Summary of Company's investment
Number of facilities | property	8
Land	$ 1,925
Buildings, Improvements,and Lease Intangibles	64,274
Personal Property	598
Total real estate properties	66,797
Accumulated Depreciation	$ (20,235)
Other [Member] | Austin, Texas [Member]
Summary of Company's investment
Number of facilities | property	1
Land	$ 1,480
Buildings, Improvements,and Lease Intangibles	3,872
Personal Property	2
Total real estate properties	5,354
Accumulated Depreciation	$ (164)
Other [Member] | Fenton, Michigan [Member]
Summary of Company's investment
Number of facilities | property	1
Land	$ 40
Buildings, Improvements,and Lease Intangibles	3,468
Personal Property	32
Total real estate properties	3,540
Accumulated Depreciation	$ (2,738)
Other [Member] | Ovid, Michigan [Member]
Summary of Company's investment
Number of facilities | property	1
Land	$ 62
Buildings, Improvements,and Lease Intangibles	3,188
Personal Property	49
Total real estate properties	3,299
Accumulated Depreciation	$ (2,096)
Other [Member] | Fremont, Michigan [Member]
Summary of Company's investment
Number of facilities | property	1
Land	$ 7
Buildings, Improvements,and Lease Intangibles	3,242
Personal Property	35
Total real estate properties	3,284
Accumulated Depreciation	$ (2,565)
Other [Member] | St. Louis, Michigan [Member]
Summary of Company's investment
Number of facilities | property	1
Land	$ 31
Buildings, Improvements,and Lease Intangibles	1,735
Personal Property	33
Total real estate properties	1,799
Accumulated Depreciation	$ 1,341
Other [Member] | Iowa [Member]
Summary of Company's investment
Number of facilities | property	1
Land	$ 0
Buildings, Improvements,and Lease Intangibles	40,354
Personal Property	5
Total real estate properties	40,359
Accumulated Depreciation	$ (7,704)
Other [Member] | Johnson City, Tennessee [Member]
Summary of Company's investment
Number of facilities | property	1
Land	$ 253
Buildings, Improvements,and Lease Intangibles	7,319
Personal Property	408
Total real estate properties	7,980
Accumulated Depreciation	$ (2,798)
Other [Member] | Detroit, Michigan [Member]
Summary of Company's investment
Number of facilities | property	1
Land	$ 52
Buildings, Improvements,and Lease Intangibles	1,096
Personal Property	34
Total real estate properties	1,182
Accumulated Depreciation	$ (829)

Property Investments (Details T

Property Investments (Details Textual) $ in Billions	Dec. 31, 2017USD ($)property
Real Estate Investment Property, Net [Abstract]
Investment in real estate properties and mortgage notes | $	$ 3.8
Number of real estate investments | property	201

Real Estate Leases (Details)

Real Estate Leases (Details) $ in Thousands	Dec. 31, 2017USD ($)
Leases [Abstract]
2,018	$ 330,526
2,019	282,910
2,020	236,454
2,021	196,346
2,022	168,183
2023 and thereafter	544,677
Total	$ 1,759,096

Real Estate Leases - Narrative

Real Estate Leases - Narrative (Details) $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2017Purchase_options	Dec. 31, 2017USD ($)renewal_option	Dec. 31, 2016	Dec. 31, 2015
Concentration Risk [Line Items]
Approximate Investment in real estate properties subject to outstanding contractual option to purchase		$ 95.2
Number of exercisable purchase options	1	4
Customer Concentration Risk [Member] | Sales Revenue, Net [Member]
Concentration Risk [Line Items]
Concentration risk (percent)		9.70%	9.80%	9.80%

Acquisitions, Dispositions an59

Acquisitions, Dispositions and Mortgage Repayments - Acquisitions (Details) $ in Millions	Dec. 21, 2017USD ($)ft²	Dec. 18, 2017USD ($)ft²Garage	Dec. 13, 2017USD ($)ft²	Nov. 01, 2017USD ($)ft²	Jul. 31, 2017USD ($)ft²	Jun. 13, 2017USD ($)ft²	Jun. 12, 2017USD ($)ft²	Mar. 06, 2017USD ($)ft²	Dec. 21, 2016USD ($)ft²	Oct. 17, 2016USD ($)ft²	Oct. 11, 2016USD ($)ft²	Sep. 26, 2016USD ($)ft²	Sep. 12, 2016USD ($)ft²	May 13, 2016USD ($)ft²	Apr. 29, 2016USD ($)ft²	Mar. 31, 2016USD ($)ft²	Dec. 31, 2017USD ($)ft²	Dec. 31, 2016USD ($)ft²
Real estate acquisitions [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Purchase Price																	$ 327.2	$ 241.9
Mortgage Notes Payable Assumed																	(45.8)	(13.2)
Cash Consideration																	283.1	224.9
Real Estate																	322.6	239.3
Other																	$ 6.3	$ (1.2)
Square Footage | ft²																	877,873	583,011
Fair value adjustments on mortgage notes payable assumed																	$ 0.6	$ (0.8)
Real estate acquisitions [Member] | Minnesota [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired								Mar. 6, 2017	Dec. 21, 2016
Purchase Price								$ 13.5	$ 12.6
Mortgage Notes Payable Assumed								0	0
Cash Consideration								13.5	12.5
Real Estate								13.3	11.3
Other								$ 0.2	$ 1.2
Square Footage | ft²								34,608	48,281
Real estate acquisitions [Member] | San Francisco, California [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired							Jun. 12, 2017
Purchase Price							$ 26.8
Mortgage Notes Payable Assumed							0
Cash Consideration							26.8
Real Estate							26.8
Other							$ 0
Square Footage | ft²							75,649
Real estate acquisitions [Member] | DISTRICT OF COLUMBIA
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired						Jun. 13, 2017						Sep. 26, 2016
Purchase Price						$ 24						$ 45.2
Mortgage Notes Payable Assumed						(12.1)						0
Cash Consideration						12.5						45.1
Real Estate						24.8						43.7
Other						$ (0.2)						$ 1.4
Square Footage | ft²						62,379						103,783
Real estate acquisitions [Member] | Maryland [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired											Oct. 11, 2016
Purchase Price											$ 36.2
Mortgage Notes Payable Assumed											0
Cash Consideration											36.4
Real Estate											36.4
Other											$ 0
Square Footage | ft²											113,631
Real estate acquisitions [Member] | Los Angeles, California [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired					Jul. 31, 2017									May 13, 2016
Purchase Price					$ 16.3									$ 20
Mortgage Notes Payable Assumed					0									(13.2)
Cash Consideration					16.7									6.5
Real Estate					16.9									20.4
Other					$ (0.2)									$ (0.7)
Square Footage | ft²					42,780									63,012
Real estate acquisitions [Member] | Washington [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired		Dec. 18, 2017		Nov. 1, 2017					Dec. 21, 2016	Oct. 17, 2016			Sep. 12, 2016		Apr. 29, 2016	Mar. 31, 2016
Purchase Price		$ 8.8		$ 12.7					$ 5.1	$ 9.8			$ 53.1		$ 21.6	$ 38.3
Mortgage Notes Payable Assumed		0		0					0	0			0		0	0
Cash Consideration		8.8		12.6					5.1	9.8			53		18.8	37.7
Real Estate		9		12.8					5.2	9.9			54.6		20.1	37.7
Other		$ (0.2)		$ (0.2)					$ (0.1)	$ (0.1)			$ (1.6)		$ (1.3)	$ 0
Square Footage | ft²		32,828		26,345					20,740	29,753			87,462		46,637	69,712
Real estate acquisitions [Member] | Illinois [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired		Dec. 18, 2017
Purchase Price		$ 28.7
Mortgage Notes Payable Assumed		0
Cash Consideration		27.7
Real Estate		28.5
Other		$ (0.8)
Square Footage | ft²		99,526
Real estate acquisitions [Member] | Texas [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired	Dec. 21, 2017
Purchase Price	$ 2.5
Mortgage Notes Payable Assumed	0
Cash Consideration	2.5
Real Estate	2.5
Other	$ 0
Square Footage | ft²	7,972
Property ownership percentage	69.40%
Real Estate Acquisition One [Member] | Georgia [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired		Dec. 18, 2017	Dec. 13, 2017	Nov. 1, 2017
Purchase Price		$ 26.3	$ 25.8	$ 25.5
Mortgage Notes Payable Assumed		(11.8)	(10.5)	0
Cash Consideration		14.5	15.3	25.5
Real Estate		24.6	22	26.3
Other		$ 1.7	$ 3.8	$ (0.8)
Square Footage | ft²		66,984	59,427	76,944
Number of parking garages | Garage		2
Real Estate Acquisition Two [Member] | Georgia [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired		Dec. 18, 2017	Dec. 13, 2017	Nov. 1, 2017
Purchase Price		$ 14.2	$ 15.4	$ 30.3
Mortgage Notes Payable Assumed		(6.7)	(4.7)	0
Cash Consideration		7.6	10.8	30.7
Real Estate		14.5	15.7	30.7
Other		$ (0.2)	$ (0.2)	$ 0
Square Footage | ft²		40,324	40,171	74,024
Real Estate Acquisition Three [Member] | Georgia [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired				Nov. 1, 2017
Purchase Price				$ 49.7
Mortgage Notes Payable Assumed				0
Cash Consideration				50.9
Real Estate				47.5
Other				$ 3.4
Square Footage | ft²				118,180
Real Estate Acquisition Four [Member] | Georgia [Member]
Real Estate Acquisitions and Mortgage Note Financing [Line Items]
Date Acquired				Nov. 1, 2017
Purchase Price				$ 6.7
Mortgage Notes Payable Assumed				0
Cash Consideration				6.7
Real Estate				6.7
Other				$ 0
Square Footage | ft²				19,732

Acquisitions, Dispositions an60

Acquisitions, Dispositions and Mortgage Repayments - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Building	$ 272.1	$ 216.8
Land	11.7	9.7
Land Improvements	1.6
Intangibles	36.7	13.7
Mortgage notes payable assumed, including fair value adjustments	(46.4)	(14)
Other assets acquired	0.4	0.5
Equity investment in joint ventures	8.7
Accounts payable, accrued liabilities and other liabilities assumed	(1.7)	(1.8)
Total cash paid	283.1	224.9
At market lease Intangibles [Member]
Business Acquisition [Line Items]
Intangibles	37.2	12.8
Above-market lease intangibles [Member]
Business Acquisition [Line Items]
Intangibles		0.9
Below-market ground lease intangibles [Member]
Business Acquisition [Line Items]
Intangibles	$ 0.4	$ 2
Minimum [Member] | At market lease Intangibles [Member]
Business Acquisition [Line Items]
Intangible asset useful life	2 years 1 month 6 days	2 years 8 months 12 days
Minimum [Member] | Above-market lease intangibles [Member]
Business Acquisition [Line Items]
Intangible asset useful life		8 months 12 days
Minimum [Member] | Below-market lease intangibles [Member]
Business Acquisition [Line Items]
Intangible asset useful life	8 years 6 months	1 year 4 months 24 days
Minimum [Member] | Below-market ground lease intangibles [Member]
Business Acquisition [Line Items]
Intangible asset useful life	36 years 9 months 18 days	36 years 9 months 18 days
Minimum [Member] | Building [Member]
Business Acquisition [Line Items]
Asset estimated useful life	15 years	20 years
Minimum [Member] | Land Improvements [Member]
Business Acquisition [Line Items]
Asset estimated useful life	5 years
Maximum [Member] | At market lease Intangibles [Member]
Business Acquisition [Line Items]
Intangible asset useful life	12 years 7 months 6 days	10 years 3 months 18 days
Maximum [Member] | Above-market lease intangibles [Member]
Business Acquisition [Line Items]
Intangible asset useful life		3 years 9 months 18 days
Maximum [Member] | Below-market lease intangibles [Member]
Business Acquisition [Line Items]
Intangible asset useful life	15 years	9 years 4 months 24 days
Maximum [Member] | Below-market ground lease intangibles [Member]
Business Acquisition [Line Items]
Intangible asset useful life	99 years	99 years
Maximum [Member] | Building [Member]
Business Acquisition [Line Items]
Asset estimated useful life	37 years	35 years
Maximum [Member] | Land Improvements [Member]
Business Acquisition [Line Items]
Asset estimated useful life	39 years
Above-market ground lease intangibles [Member]
Business Acquisition [Line Items]
Intangible liabilities		$ (1.6)
Intangible asset useful life		99 years
Below-market lease intangibles [Member]
Business Acquisition [Line Items]
Intangible liabilities	$ (0.9)	$ (0.4)
2017 Acquisitions [Member] | Minimum [Member] | Land Improvements [Member]
Business Acquisition [Line Items]
Asset estimated useful life	5 years
2017 Acquisitions [Member] | Maximum [Member] | Land Improvements [Member]
Business Acquisition [Line Items]
Asset estimated useful life	12 years

Acquisitions, Dispositions an61

Acquisitions, Dispositions and Mortgage Repayments - Dispositions (Details) $ in Thousands	Sep. 07, 2017USD ($)ft²	Jun. 29, 2017USD ($)ft²	Jun. 16, 2017USD ($)ft²	Mar. 31, 2017USD ($)ft²	Mar. 30, 2017USD ($)ft²	Mar. 07, 2017USD ($)ft²	Mar. 06, 2017USD ($)ft²	Dec. 22, 2016USD ($)ft²	Dec. 20, 2016USD ($)ft²	Oct. 28, 2016USD ($)ft²	Oct. 14, 2016USD ($)ft²	Mar. 31, 2017USD ($)ft²	Dec. 31, 2017USD ($)ft²	Dec. 31, 2016USD ($)ft²	Dec. 31, 2015USD ($)	Oct. 31, 2017USD ($)
Real Estate Dispositions [Line Items]
Sales Price													$ 122,700	$ 94,700		$ 45,500
Closing Adjustments													(3,300)	(1,400)
Net Proceeds													119,400	93,300
Net Real Estate Investment													78,200	49,400
Other (including receivables)													6,800	2,900
Gain/ (Impairment)													$ 34,400	$ 41,000
Square Footage | ft²													416,481	320,702
Impairment of real estate													$ 5,385		$ 3,639
Indiana [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed							Mar. 6, 2017
Sales Price							$ 6,400
Closing Adjustments							0
Net Proceeds							6,400
Net Real Estate Investment							1,100
Other (including receivables)							0
Gain/ (Impairment)							$ 5,300
Square Footage | ft²							29,500
Georgia [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed						Mar. 7, 2017		Dec. 22, 2016
Sales Price						$ 600		$ 2,800
Closing Adjustments						0		(200)
Net Proceeds						600		2,600
Net Real Estate Investment						600		1,800
Other (including receivables)						0		0
Gain/ (Impairment)						$ 0		$ 800
Square Footage | ft²						12,000		8,749
Nevada [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed					Mar. 30, 2017
Sales Price					$ 5,500
Closing Adjustments					(700)
Net Proceeds					4,800
Net Real Estate Investment					2,200
Other (including receivables)					300
Gain/ (Impairment)					$ 2,300
Square Footage | ft²					18,147
Texas [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed				Mar. 31, 2017
Sales Price				$ 69,500								$ 69,500
Closing Adjustments				(1,600)								(1,600)
Net Proceeds				67,900
Net Real Estate Investment				46,900								46,900
Other (including receivables)				5,200								$ 5,200
Gain/ (Impairment)				$ 15,800
Square Footage | ft²				169,722								169,722
Illinois [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed			Jun. 16, 2017
Sales Price			$ 500
Closing Adjustments			(100)
Net Proceeds			400
Net Real Estate Investment			400
Other (including receivables)			0
Gain/ (Impairment)			$ 0
Square Footage | ft²			5,100
Impairment of real estate												$ 300
San Antonio, Texas [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed		Jun. 29, 2017
Sales Price		$ 14,500
Closing Adjustments		(200)
Net Proceeds		14,300
Net Real Estate Investment		5,100
Other (including receivables)		900
Gain/ (Impairment)		$ 8,300
Square Footage | ft²		39,786
Oregon [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed		Jun. 29, 2017
Sales Price		$ 23,200
Closing Adjustments		(600)
Net Proceeds		22,600
Net Real Estate Investment		14,500
Other (including receivables)		300
Gain/ (Impairment)		$ 7,800
Square Footage | ft²		62,246
Missouri [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed	Sep. 7, 2017
Sales Price	$ 2,500
Closing Adjustments	(100)
Net Proceeds	2,400
Net Real Estate Investment	7,400
Other (including receivables)	100
Gain/ (Impairment)	$ (5,100)
Square Footage | ft²	79,980
Kansas [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed											Oct. 14, 2016
Sales Price											$ 15,100
Closing Adjustments											0
Net Proceeds											15,100
Net Real Estate Investment											7,200
Other (including receivables)											300
Gain/ (Impairment)											$ 7,600
Square Footage | ft²											70,908
Tennessee [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed										Oct. 28, 2016
Sales Price										$ 8,800
Closing Adjustments										(200)
Net Proceeds										8,600
Net Real Estate Investment										6,300
Other (including receivables)										200
Gain/ (Impairment)										$ 2,100
Square Footage | ft²										45,274
Altoona, Pennsylvania [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed									Dec. 20, 2016
Sales Price									$ 21,500
Closing Adjustments									(400)
Net Proceeds									21,100
Net Real Estate Investment									12,400
Other (including receivables)									600
Gain/ (Impairment)									$ 8,100
Square Footage | ft²									64,032
Harrisburg, Pennsylvania [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed									Dec. 20, 2016
Sales Price									$ 24,200
Closing Adjustments									(600)
Net Proceeds									23,600
Net Real Estate Investment									8,200
Other (including receivables)									400
Gain/ (Impairment)									$ 15,000
Square Footage | ft²									79,836
Arizona [Member] | Real estate dispositions [Member]
Real Estate Dispositions [Line Items]
Date Disposed									Dec. 20, 2016
Sales Price									$ 22,300
Closing Adjustments									0
Net Proceeds									22,300
Net Real Estate Investment									13,500
Other (including receivables)									1,400
Gain/ (Impairment)									$ 7,400
Square Footage | ft²									51,903

Acquisitions, Dispositions an62

Acquisitions, Dispositions and Mortgage Repayments - Additional information (Details) $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2017USD ($)propertybuildingPurchase_options	Dec. 31, 2017USD ($)renewal_option	Dec. 31, 2016USD ($)
Acquisitions and Dispositions and Mortgage Repayments [Abstract]
Number of properties exercising purchase option | property	7
Number of single-tenant net leased buildings exercising purchase option | building	5
Number of multi-tenant buildings exercisng purchase option | building	2
Number of purchase options	1	4
Stated purchase price | $	$ 45.5	$ 122.7	$ 94.7
Aggregate net book value of potential dispositions | $		$ 23.9

Held for Sale and Discontinue63

Held for Sale and Discontinued Operations (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Balance Sheet data (as of the period ended):
Land	$ 201,283	$ 199,672
Buildings, improvements and lease intangibles	3,601,460	3,386,480
Personal property	10,314	10,291
Total real estate properties	3,838,638	3,628,221
Less accumulated depreciation	(897,430)	(840,839)
Total real estate properties, net	2,941,208	2,787,382
Other assets, net (including receivables)	213,015	195,666
Assets held for sale and discontinued operations, net	33,147	3,092
Liabilities of assets held for sale and discontinued operations	93	614
Discontinued Operations [Member]
Balance Sheet data (as of the period ended):
Land	4,636	1,362
Buildings, improvements and lease intangibles	63,654	4,410
Personal property	82	0
Total real estate properties	68,372	5,772
Less accumulated depreciation	(35,790)	(2,977)
Total real estate properties, net	32,582	2,795
Other assets, net (including receivables)	565	297
Assets of discontinued operations, net	565	297
Assets held for sale and discontinued operations, net	33,147	3,092
Accounts payable and accrued liabilities	38	22
Other liabilities	55	592
Liabilities of assets held for sale and discontinued operations	$ 93	$ 614

Held for Sale and Discontinue64

Held for Sale and Discontinued Operations (Details 1) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Rental income									$ 422,852	$ 407,481	$ 383,333
Other operating									1,647	4,149	5,047
Expenses
Property operating									157,233	146,458	140,195
Bad debt, net of recoveries									169	(21)	(193)
Other Income (Expense)
Interest and other income, net									896	375	389
Income from discontinued operations									(9)	(71)	715
Impairments										(121)	(686)
Gain on sales of real estate properties									5	7	10,571
INCOME (LOSS) FROM DISCONTINUED OPERATIONS	$ 0	$ 8	$ 0	$ (13)	$ (143)	$ (23)	$ (12)	$ (7)	$ (4)	$ (185)	$ 10,600
Income (Loss) from Discontinued Operations per Common Share - Basic (in dollars per share)									$ 0	$ 0	$ 0.11
Income (Loss) from Discontinued Operations per Common Share - Diluted (in dollars per share)									$ 0	$ 0	$ 0.11
Discontinued Operations [Member]
Revenues
Rental income									$ 0	$ 0	$ 752
Other operating									0	0	0
Total Revenue									0	0	752
Expenses
Property operating									19	71	58
Bad debt, net of recoveries									(10)	0	(1)
Total Expense									9	71	57
Other Income (Expense)
Interest and other income, net									0	0	20
Total other income (expense)									0	0	20
Income from discontinued operations									(9)	(71)	715
Impairments									0	(121)	(686)
Gain on sales of real estate properties									5	7	10,571
INCOME (LOSS) FROM DISCONTINUED OPERATIONS									$ (4)	$ (185)	$ 10,600
Income (Loss) from Discontinued Operations per Common Share - Basic (in dollars per share)									$ 0	$ 0	$ 0.11
Income (Loss) from Discontinued Operations per Common Share - Diluted (in dollars per share)									$ 0	$ 0	$ 0.11

Held for Sale and Discontinue65

Held for Sale and Discontinued Operations (Details Textual) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Oct. 31, 2017property	Dec. 31, 2017propertyProperty	Dec. 31, 2017property	Dec. 31, 2016USD ($)property	Dec. 31, 2015USD ($)property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties reclassified to held for sale | Property		8
Number of properties exercising purchase option	7
Number of properties held for sale		8	8	2
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue related to properties sold | $					$ 0.8
Expenses related to sale of real estate | $				$ 0.1	0.1
Impairments related to property held for sale | $				$ 0.1	$ 0.7
Number of impaired properties held for sale				1
Number of properties related to gain on sales			1	1	1

Impairment Charges (Details Tex

Impairment Charges (Details Textual) $ in Thousands	3 Months Ended			12 Months Ended
	Jun. 30, 2017property	Mar. 31, 2017property	Dec. 31, 2016property	Dec. 31, 2017USD ($)property	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)property
Property, Plant and Equipment [Abstract]
Impairments					$ 121	$ 686
Number of properties sold | property	3	6	6	2		2
Impairment of real estate				$ 5,385		$ 3,639

Other Assets (Details)

Other Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid assets	$ 65,200	$ 64,800
Equity investment in joint ventures	8,700	0
Straight-line rent receivables	67,000	64,600
Above-market intangible assets, net	17,900	19,100
Additional long-lived assets, net	24,900	14,500
Ground lease modification, net	10,300	10,800
Accounts receivable	7,400	8,100
Allowance for uncollectible accounts	(300)	(100)
Credit facility deferred financing costs	3,500	4,900
Goodwill	3,487	3,487
Customer relationship intangible assets, net	1,700	1,800
Other	3,200	3,700
Other Assets	$ 213,015	$ 195,666

Other Assets - Unconsolidated J

Other Assets - Unconsolidated Joint Ventures (Details) $ in Thousands	3 Months Ended			12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2017Garage	Dec. 31, 2017building	Dec. 31, 2017USD ($)
Equity Method Investments [Roll Forward]
Net LLC investment, beginning of period				$ 0
Equity income (loss) recognized during the period				7
Net LLC investments, end of period	$ 8,700			8,700
Parking Garages [Member]
Property, Plant and Equipment [Line Items]
Number of parking garages		2	2
Number of buildings acquired | building			3
Equity Method Investments [Roll Forward]
Net LLC investment, beginning of period				0
New investments during the period	8,700			8,700
Equity income (loss) recognized during the period				0
Net LLC investments, end of period	$ 8,700			$ 8,700

Intangible Assets and Liabili69

Intangible Assets and Liabilities - Components of intangible assets and liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule of finite lived intangible assets and liabilities
Intangible assets and liabilities, gross	$ 144.2	$ 120.7
Intangible assets and liabilities, accumulated amortization	$ 47.7	46.5
Assets and liabilities, weighted avg. life (years)	15 years 2 months
Below-market lease intangibles [Member] | Other liabilities [Member]
Schedule of finite lived intangible assets and liabilities
Liabilities gross balance	$ (9.5)	(8.8)
Liabilities accumulated amortization	$ (3.5)	(3.2)
Liabilities, weighted avg. life (years)	36 years 6 months
Deferred financing costs [Member] | Other liabilities [Member]
Schedule of finite lived intangible assets and liabilities
Liabilities gross balance	$ 9.3	9.4
Liabilities accumulated amortization	$ 1.8	4
Liabilities, weighted avg. life (years)	4 years 6 months
Goodwill [Member] | Other assets [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	$ 3.5	3.5
Assets accumulated amortization	0	0
Deferred financing costs [Member] | Other assets [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	5.4	5.4
Assets accumulated amortization	$ 1.9	0.5
Assets, weighted avg. life (years)	2 years 7 months 6 days
Above-market lease intangibles [Member] | Other assets [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	$ 22.9	24.5
Assets accumulated amortization	$ 5	5.4
Assets, weighted avg. life (years)	57 years 9 months 18 days
Customer relationship intangibles [Member] | Other assets [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	$ 2.6	2.6
Assets accumulated amortization	$ 0.9	0.8
Assets, weighted avg. life (years)	25 years 7 months 6 days
At market lease Intangibles [Member] | Real estate properties [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	$ 110	84.1
Assets accumulated amortization	$ 41.6	$ 39
Assets, weighted avg. life (years)	5 years 7 months 6 days

Intangible Assets and Liabili70

Intangible Assets and Liabilities - Expected future amortization expense (Details) $ in Millions	Dec. 31, 2017USD ($)
Future Amortization of Intangibles, Net [Abstract]
2,018	$ 19.8
2,019	17.6
2,020	12
2,021	6.8
2,022	$ 5.8

Notes and Bonds Payable (Detail

Notes and Bonds Payable (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 11, 2017	Dec. 31, 2016USD ($)	Apr. 24, 2015	Mar. 26, 2013
Debt Instrument [Line Items]
Notes and bonds payable	$ 1,283,880,000	$ 1,283,880,000		$ 1,264,370,000
Line of Credit [Member] | Unsecured Credit Facility [Member]
Debt Instrument [Line Items]
Notes and bonds payable	189,000,000	189,000,000		107,000,000
Medium-term Notes [Member] | Unsecured Term Loan due 2022 [Member]
Debt Instrument [Line Items]
Notes and bonds payable	$ 148,994,000	$ 148,994,000		149,491,000
Contractual interest rates, basis spread on variable rate		1.10%
Senior Notes [Member] | Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Extinguishment of debt, number of transactions	2
Notes and bonds payable	$ 0	$ 0		397,147,000
Contractual interest rates	5.75%	5.75%
Senior Notes [Member] | Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Notes and bonds payable	$ 247,703,000	$ 247,703,000		247,296,000
Contractual interest rates	3.75%	3.75%				3.75%
Senior Notes [Member] | Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Notes and bonds payable	$ 248,044,000	$ 248,044,000		247,819,000
Contractual interest rates	3.88%	3.88%			3.875%
Senior Notes [Member] | Senior Notes due 2028 [Member]
Debt Instrument [Line Items]
Notes and bonds payable	$ 294,757,000	$ 294,757,000		0
Contractual interest rates	3.63%	3.63%	3.625%
Mortgage Notes [Member] | Mortgage notes payable [Member]
Debt Instrument [Line Items]
Notes and bonds payable	$ 155,382,000	$ 155,382,000		$ 115,617,000
LIBOR [Member] | Line of Credit [Member] | Unsecured Credit Facility [Member]
Debt Instrument [Line Items]
Contractual interest rates, basis spread on variable rate		1.00%
LIBOR [Member] | Medium-term Notes [Member] | Unsecured Term Loan due 2022 [Member]
Debt Instrument [Line Items]
Contractual interest rates, basis spread on variable rate		1.10%
Minimum [Member] | Medium-term Notes [Member] | Unsecured Term Loan due 2022 [Member]
Debt Instrument [Line Items]
Contractual interest rates, basis spread on variable rate		0.90%
Minimum [Member] | Mortgage Notes [Member]
Debt Instrument [Line Items]
Contractual interest rates	3.30%	3.30%
Minimum [Member] | Mortgage Notes [Member] | Mortgage notes payable [Member]
Debt Instrument [Line Items]
Contractual interest rates	3.31%	3.31%
Maximum [Member] | Medium-term Notes [Member] | Unsecured Term Loan due 2022 [Member]
Debt Instrument [Line Items]
Contractual interest rates, basis spread on variable rate		1.75%
Maximum [Member] | Mortgage Notes [Member]
Debt Instrument [Line Items]
Contractual interest rates	6.90%	6.90%
Maximum [Member] | Mortgage Notes [Member] | Mortgage notes payable [Member]
Debt Instrument [Line Items]
Contractual interest rates	6.88%	6.88%

Notes and Bonds Payable - Narra

Notes and Bonds Payable - Narrative (Details)	Dec. 27, 2017USD ($)	Nov. 01, 2017USD ($)	Jul. 05, 2016USD ($)	Apr. 24, 2015USD ($)swap_agreement	Feb. 15, 2013extension_option	Dec. 31, 2017USD ($)swap_agreement	Dec. 31, 2017USD ($)swap_agreement	Dec. 31, 2017USD ($)swap_agreement	Dec. 31, 2016USD ($)swap_agreement	Dec. 31, 2015USD ($)swap_agreement	Jan. 30, 2018USD ($)swap_agreementderivative	Dec. 20, 2017USD ($)swap_agreement	Dec. 18, 2017Lender	Dec. 11, 2017USD ($)	Feb. 28, 2014USD ($)Lender	Mar. 26, 2013USD ($)	Oct. 14, 2011USD ($)
Debt Instrument [Line Items]
Number of interest rate swaps | swap_agreement						2	2	2
Unsecured term loan outstanding						$ 1,293,916,000	$ 1,293,916,000	$ 1,293,916,000
Interest paid								64,395,000	$ 55,878,000	$ 69,773,000
Loss on extinguishment of debt							45,000,000	$ (44,985,000)		$ (27,998,000)
Number of forward starting swaps | swap_agreement								4	4	4
Subsequent Event [Member]
Debt Instrument [Line Items]
Number of interest rate swaps | derivative											2
Line of Credit [Member] | Unsecured Credit Facility [Member]
Debt Instrument [Line Items]
Unsecured credit facility																	$ 700,000,000
Number of extension options | extension_option					2
Period of extension option					6 months
Extension fees as percentage of aggregate commitments					0.075%
Facility fee on the aggregate amount of commitments								0.20%
Amount outstanding under Unsecured Credit Facility						$ 189,000,000	$ 189,000,000	$ 189,000,000
Weighted average interest rate (LOC)						2.56%	2.56%	2.56%
Remaining borrowing capacity						$ 511,000,000	$ 511,000,000	$ 511,000,000
Line of Credit [Member] | Unsecured Credit Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Facility fee on the aggregate amount of commitments								0.13%
Line of Credit [Member] | Unsecured Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Facility fee on the aggregate amount of commitments								0.30%
Line of Credit [Member] | Unsecured Credit Facility [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Percentage of interest in addition to LIBOR								1.00%
Contractual interest rates, basis spread on variable rate								1.00%
Line of Credit [Member] | Unsecured Credit Facility [Member] | LIBOR [Member] | Minimum [Member]
Debt Instrument [Line Items]
Percentage of interest in addition to LIBOR								0.83%
Line of Credit [Member] | Unsecured Credit Facility [Member] | LIBOR [Member] | Maximum [Member]
Debt Instrument [Line Items]
Percentage of interest in addition to LIBOR								1.55%
Medium-term Notes [Member] | Term Loan due 2022 [Member]
Debt Instrument [Line Items]
Weighted average interest rate (LOC)						2.77%	2.77%	2.77%
Senior notes face value															$ 200,000,000
Number of lenders, term loan | Lender													9		9
Amount of debt repaid			$ 50,000,000
Contractual interest rates, basis spread on variable rate								1.10%
Number of interest rate swaps | swap_agreement												2
Unsecured term loan outstanding						$ 150,000,000	$ 150,000,000	$ 150,000,000
Medium-term Notes [Member] | Term Loan due 2022 [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Number of interest rate swaps | swap_agreement											2
Derivative notional amount											$ 50,000,000
Derivative, fixed interest rate											2.46%
Medium-term Notes [Member] | Term Loan due 2022 [Member] | Interest Rate Swap [Member]
Debt Instrument [Line Items]
Derivative notional amount												$ 25,000,000
Derivative, fixed interest rate												2.18%
Medium-term Notes [Member] | Term Loan due 2022 [Member] | Minimum [Member]
Debt Instrument [Line Items]
Contractual interest rates, basis spread on variable rate								0.90%
Medium-term Notes [Member] | Term Loan due 2022 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Contractual interest rates, basis spread on variable rate								1.75%
Medium-term Notes [Member] | Term Loan due 2022 [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Contractual interest rates, basis spread on variable rate								1.10%
Senior Notes [Member] | Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Senior notes face value						0	0	$ 0	$ 400,000,000
Amount of debt repaid	$ 300,000,000	$ 100,000,000				400,000,000	$ 400,000,000
Extinguishment of debt, number of transactions							2
Aggregate redemption price of debt						452,300,000
Interest paid						9,500,000
Make-whole payment on early extinguishment of debt						42,800,000
Write off of unamortized deferred financing costs						2,200,000
Loss on extinguishment of debt						$ 45,000,000
Interest rate on senior notes						5.75%	5.75%	5.75%
Unaccreted discount						$ 0	$ 0	$ 0	1,510,000
Senior Notes [Member] | Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Senior notes face value						$ 250,000,000	$ 250,000,000	$ 250,000,000	250,000,000							$ 250,000,000
Interest rate on senior notes						3.75%	3.75%	3.75%								3.75%
Unaccreted discount						$ 1,178,000	$ 1,178,000	$ 1,178,000	1,375,000							$ 2,100,000
Deferred finance costs, gross																$ 2,100,000
Interest rate yielded per annum upon issuance																3.95%
Amount of amortization included in interest expense on the Company's consolidated Statements of operations								200,000	200,000	$ 200,000
Amortization of debt issuance costs								200,000	200,000	200,000
Senior Notes [Member] | Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Senior notes face value				$ 250,000,000		$ 250,000,000	$ 250,000,000	$ 250,000,000	250,000,000
Interest rate on senior notes				3.875%		3.88%	3.88%	3.88%
Unaccreted discount				$ 200,000		$ 160,000	$ 160,000	$ 160,000	178,000
Deferred finance costs, gross				$ 2,300,000
Interest rate yielded per annum upon issuance				4.08%
Amortization of debt issuance costs								200,000	200,000	100,000
Number of forward starting swaps | swap_agreement				4
Senior Notes [Member] | Senior Notes due 2025 [Member] | Interest Rate Swap [Member]
Debt Instrument [Line Items]
Loss on forward starting interest rate swap agreements recognized in OCI				$ 1,700,000
Senior Notes [Member] | Senior Notes due 2028 [Member]
Debt Instrument [Line Items]
Senior notes face value						$ 300,000,000	$ 300,000,000	$ 300,000,000						$ 300,000,000
Interest rate on senior notes						3.63%	3.63%	3.63%						3.625%
Unaccreted discount						$ 2,529,000	$ 2,529,000	$ 2,529,000						$ 2,500,000
Deferred finance costs, gross														$ 2,700,000
Interest rate yielded per annum upon issuance														3.84%
Mortgage Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate on senior notes						3.30%	3.30%	3.30%
Mortgage Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest rate on senior notes						6.90%	6.90%	6.90%
Mortgage Notes [Member] | Mortgage notes payable [Member]
Debt Instrument [Line Items]
Senior notes face value						$ 154,916,000	$ 154,916,000	$ 154,916,000	114,934,000
Unaccreted discount						$ 1,332,000	$ 1,332,000	1,332,000	1,450,000
Amortization of debt issuance costs								100,000	200,000	200,000
Amortization of debt discount								300,000	300,000	800,000
Amortization of debt premium								$ 700,000	$ 900,000	$ 1,000,000
Mortgage Notes [Member] | Mortgage notes payable [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate on senior notes						3.31%	3.31%	3.31%
Mortgage Notes [Member] | Mortgage notes payable [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest rate on senior notes						6.88%	6.88%	6.88%

Notes and Bonds Payable - Senio

Notes and Bonds Payable - Senior Notes (Details) - USD ($)	Dec. 31, 2017	Dec. 11, 2017	Dec. 31, 2016	Apr. 24, 2015	Mar. 26, 2013
Debt Instrument [Line Items]
Issuance costs	$ (7,488,000)
Notes and bonds payable	1,283,880,000		$ 1,264,370,000
Senior Notes [Member] | Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Senior notes face value	0		400,000,000
Unaccreted discount	0		(1,510,000)
Issuance costs	0		(1,343,000)
Notes and bonds payable	0		397,147,000
Senior Notes [Member] | Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Senior notes face value	250,000,000		250,000,000		$ 250,000,000
Unaccreted discount	(1,178,000)		(1,375,000)		$ (2,100,000)
Issuance costs	(1,119,000)		(1,329,000)
Notes and bonds payable	247,703,000		247,296,000
Senior Notes [Member] | Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Senior notes face value	250,000,000		250,000,000	$ 250,000,000
Unaccreted discount	(160,000)		(178,000)	$ (200,000)
Issuance costs	(1,796,000)		(2,003,000)
Notes and bonds payable	248,044,000		247,819,000
Senior Notes [Member] | Senior Notes due 2028 [Member]
Debt Instrument [Line Items]
Senior notes face value	300,000,000	$ 300,000,000
Unaccreted discount	(2,529,000)	$ (2,500,000)
Issuance costs	(2,714,000)
Notes and bonds payable	$ 294,757,000		$ 0

Notes and Bonds Payable - Mortg

Notes and Bonds Payable - Mortgage Notes (Details) $ in Thousands	Dec. 31, 2017USD ($)mortgage_note_payable	Dec. 31, 2016USD ($)
Debt Instrument [Line Items]
Issuance costs	$ (7,488)
Notes and bonds payable	$ 1,283,880	$ 1,264,370
Number of Outstanding Mortgage Notes | mortgage_note_payable	18
Mortgage Notes [Member]
Debt Instrument [Line Items]
Issuance costs	$ (900)
Number of Outstanding Mortgage Notes | mortgage_note_payable	19
Mortgage notes payable [Member] | Mortgage Notes [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 154,916	114,934
Unamortized premium	2,651	2,569
Unaccreted discount	(1,332)	(1,450)
Issuance costs	(853)	(436)
Notes and bonds payable	155,382	$ 115,617
Municipal Government [Member] | Mortgage Notes 4.79% [Member] | Mortgage Notes [Member]
Debt Instrument [Line Items]
Mortgage notes	11,000
Unamortized premium	$ 1,000
Number of Outstanding Mortgage Notes | mortgage_note_payable	3

Notes and Bonds Payable - Detai

Notes and Bonds Payable - Details of Mortgage Notes (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)mortgage_note_payable	Dec. 31, 2016USD ($)
Debt Instrument [Line Items]
Number of outstanding mortgage notes | mortgage_note_payable	18
Mortgage Notes [Member]
Debt Instrument [Line Items]
Investment in Collateral	$ 400.9
Mortgage notes payable carrying amount	$ 155.4	$ 115.6
Number of outstanding mortgage notes | mortgage_note_payable	19
Mortgage Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Contractual interest rates	6.90%
Mortgage Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Contractual interest rates	3.30%
Mortgage Notes [Member] | Mortgage Notes 5.53% [Member] | Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 7
Effective Interest rate	5.53%
Maturity Date	2018-01
Collateral	MOB
Principal and Interest Payments	Monthly/15-yr amort.
Principal and interest amortization period	15 years
Investment in Collateral	$ 0
Mortgage notes payable carrying amount	0	0.7
Unemcumbered gross investment	14.3
Mortgage Notes [Member] | Mortgage Notes 5.55% [Member] | Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 1.8
Effective Interest rate	5.55%
Maturity Date	2030-10
Collateral	OTH
Principal and Interest Payments	Monthly/27-yr amort.
Principal and interest amortization period	27 years
Investment in Collateral	$ 0
Mortgage notes payable carrying amount	0	1.3
Unemcumbered gross investment	8
Mortgage Notes [Member] | Mortgage Notes 5.54% [Member] | Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 7.3
Effective Interest rate	5.54%
Maturity Date	2018-12
Collateral	MOB
Principal and Interest Payments	Monthly/25-yr amort.
Principal and interest amortization period	25 years
Investment in Collateral	$ 14.3
Mortgage notes payable carrying amount	6	6.2
Unamortized premium	0.6
Mortgage Notes [Member] | Mortgage Notes 5.07% [Member] | Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 9.5
Effective Interest rate	5.07%
Maturity Date	2019-03
Collateral	MOB
Principal and Interest Payments	Monthly/5-yr amort.
Principal and interest amortization period	5 years
Investment in Collateral	$ 13.9
Mortgage notes payable carrying amount	9.3	9.5
Unamortized premium	0.2
Mortgage Notes [Member] | Mortgage Notes 4.55% [Member] | Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 9.4
Effective Interest rate	4.55%
Maturity Date	2019-07
Collateral	MOB
Principal and Interest Payments	Monthly/8-yr amort
Principal and interest amortization period	8 years
Investment in Collateral	$ 27.8
Mortgage notes payable carrying amount	9.2	9.3
Unamortized premium	0.3
Mortgage Notes [Member] | Mortgage Notes 7.65% [Member] | Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 15.2
Effective Interest rate	7.65%
Maturity Date	2020-07
Collateral	MOB
Principal and Interest Payments	(21)
Principal and interest amortization period	11 years
Investment in Collateral	$ 20.2
Mortgage notes payable carrying amount	12.7	12.7
Unaccreted discount	$ 2.4
Period for monthly installments of interest	24 months
Mortgage Notes [Member] | Mortgage Notes 4.00% [Member] | Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 7.9
Effective Interest rate	4.00%
Maturity Date	2020-08
Collateral	MOB
Principal and Interest Payments	Monthly/15-yr amort.
Principal and interest amortization period	15 years
Investment in Collateral	$ 20.7
Mortgage notes payable carrying amount	2	2.7
Unamortized premium	0.3
Mortgage Notes [Member] | Mortgage Notes 5.25% [Member] | Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 7.3
Effective Interest rate	5.25%
Maturity Date	2020-08
Collateral	MOB
Principal and Interest Payments	Monthly/27-yr amort.
Principal and interest amortization period	27 years
Investment in Collateral	$ 17.9
Mortgage notes payable carrying amount	6.5	6.7
Unamortized premium	0.4
Mortgage Notes [Member] | Mortgage Notes 4.27% [Member] | Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 5.6
Effective Interest rate	4.27%
Maturity Date	2021-01
Collateral	MOB
Principal and Interest Payments	Monthly/10-yr amort.
Principal and interest amortization period	10 years
Investment in Collateral	$ 15.7
Mortgage notes payable carrying amount	4.8	0
Unamortized premium	0.2
Mortgage Notes [Member] | Mortgage Notes 6.43% [Member] | Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 12.9
Effective Interest rate	6.43%
Maturity Date	2021-02
Collateral	MOB
Principal and Interest Payments	Monthly/12-yr amort.
Principal and interest amortization period	12 years
Investment in Collateral	$ 54.9
Mortgage notes payable carrying amount	10.5	10.7
Unaccreted discount	1
Mortgage Notes [Member] | Mortgage Notes 3.85% [Member] | Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 11
Effective Interest rate	3.85%
Maturity Date	2022-11
Collateral	MOB
Principal and Interest Payments	Monthly/7-yr amort.
Principal and interest amortization period	7 years
Investment in Collateral	$ 22
Mortgage notes payable carrying amount	10.4	0
Unaccreted discount	0.1
Mortgage Notes [Member] | Mortgage Notes 3.85% [Member] | Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 12.3
Effective Interest rate	3.85%
Maturity Date	2023-08
Collateral	MOB
Principal and Interest Payments	Monthly/7-yr amort.
Principal and interest amortization period	7 years
Investment in Collateral	$ 24.6
Mortgage notes payable carrying amount	11.5	0
Unaccreted discount	0.2
Mortgage Notes [Member] | Mortgage Notes 4.27% [Member] | Financial Services [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 12.4
Effective Interest rate	4.27%
Maturity Date	2023-10
Collateral	MOB
Principal and Interest Payments	Monthly/10-yr amort.
Principal and interest amortization period	10 years
Investment in Collateral	$ 24.7
Mortgage notes payable carrying amount	12.2	0
Unamortized premium	0.4
Mortgage Notes [Member] | Mortgage Notes 4.13% [Member] | Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 13.3
Effective Interest rate	4.13%
Maturity Date	2024-01
Collateral	MOB
Principal and Interest Payments	Monthly/10-yr amort.
Principal and interest amortization period	10 years
Investment in Collateral	$ 21.1
Mortgage notes payable carrying amount	13.3	13.6
Unamortized premium	0.8
Mortgage Notes [Member] | Mortgage Notes 3.94% [Member] | Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 6.8
Effective Interest rate	3.94%
Maturity Date	2024-02
Collateral	MOB
Principal and Interest Payments	Monthly/7-yr amort.
Principal and interest amortization period	7 years
Investment in Collateral	$ 14.5
Mortgage notes payable carrying amount	6.7	0
Unamortized premium	0.2
Mortgage Notes [Member] | Mortgage Notes 4.32% [Member] | Financial Services [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 9.7
Effective Interest rate	4.32%
Maturity Date	2024-09
Collateral	MOB
Principal and Interest Payments	Monthly/10-yr amort.
Principal and interest amortization period	10 years
Investment in Collateral	$ 16.4
Mortgage notes payable carrying amount	8.8	9.1
Unamortized premium	0.1
Mortgage Notes [Member] | Mortgage Notes 3.71% [Member] | Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 11.5
Effective Interest rate	3.71%
Maturity Date	2026-01
Collateral	MOB
Principal and Interest Payments	Monthly/10-yr amort.
Principal and interest amortization period	10 years
Investment in Collateral	$ 37.9
Mortgage notes payable carrying amount	10.5	11
Mortgage Notes [Member] | Mortgage Notes 5.25% 20 Year [Member] | Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 15
Effective Interest rate	5.25%
Maturity Date	2027-04
Collateral	MOB
Principal and Interest Payments	Monthly/20-yr amort.
Principal and interest amortization period	20 years
Investment in Collateral	$ 33.4
Mortgage notes payable carrying amount	9.6	10.4
Unamortized premium	0.7
Mortgage Notes [Member] | Mortgage Notes 4.79% [Member] | Municipal Government [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 11
Effective Interest rate	4.79%
Collateral	MOB
Principal and Interest Payments	Semi-Annual (20)
Investment in Collateral	$ 20.9
Mortgage notes payable carrying amount	11.4	$ 11.7
Unamortized premium	$ 1
Number of outstanding mortgage notes | mortgage_note_payable	3

Notes and Bonds Payable - Futur

Notes and Bonds Payable - Future Maturities (Details) $ in Thousands	Dec. 31, 2017USD ($)mortgage_note_payable	Dec. 31, 2016USD ($)
Long Term Debt Maturities [Line Items]
Number of outstanding mortgage notes | mortgage_note_payable	18
Excluded debt issuance costs	$ 3,500
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	1,293,916
Net Accretion/Amortization	(2,548)
Debt Issuance Costs (2)	(7,488)
Notes and bonds payable	$ 1,283,880	$ 1,264,370
%	100.00%
2018 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	$ 10,605
Net Accretion/Amortization	(18)
Debt Issuance Costs (2)	(1,051)
Notes and bonds payable	$ 9,536
%	0.70%
2019 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	$ 22,711
Net Accretion/Amortization	(224)
Debt Issuance Costs (2)	(1,044)
Notes and bonds payable	$ 21,443
%	1.70%
2020 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	$ 211,803
Net Accretion/Amortization	(382)
Debt Issuance Costs (2)	(1,039)
Notes and bonds payable	$ 210,382
%	16.40%
2021 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	$ 17,321
Net Accretion/Amortization	(312)
Debt Issuance Costs (2)	(1,025)
Notes and bonds payable	$ 15,984
%	1.20%
2022 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	$ 162,692
Net Accretion/Amortization	(328)
Debt Issuance Costs (2)	(1,037)
Notes and bonds payable	$ 161,327
%	12.60%
2023 and thereafter [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	$ 868,784
Net Accretion/Amortization	(1,284)
Debt Issuance Costs (2)	(2,292)
Notes and bonds payable	$ 865,208
%	67.40%

Derivative Financial Instrume77

Derivative Financial Instruments (Details)	12 Months Ended
	Dec. 31, 2017USD ($)swap_agreement	Dec. 31, 2016swap_agreement	Dec. 31, 2015USD ($)swap_agreement	Jan. 30, 2018USD ($)derivative
Derivative [Line Items]
Number of forward starting swaps | swap_agreement	4	4	4
Derivatives in a net liability position	$ 100,000
Derivative termination value	100,000
Interest rate cash flow hedge gain (loss) to be reclassified to interest expense during the next 12 months	$ (300,000)
Number of interest rate derivatives | swap_agreement	2
Cash Flow Hedging [Member] | Forward Starting Interest Rate Swap [Member]
Derivative [Line Items]
Notional value			$ 225,000,000
Subsequent Event [Member]
Derivative [Line Items]
Number of interest rate derivatives | derivative				2
Subsequent Event [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Notional value				$ 50,000,000

Derivative Financial Instrume78

Derivative Financial Instruments - Derivative Instruments Designated as Cash Flow Hedges (Details) $ in Millions	Dec. 31, 2017USD ($)swap_agreement
Derivative [Line Items]
Number of interest rate swaps	2
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Number of interest rate swaps	2
Derivative notional amount | $	$ 25

Derivative Financial Instrume79

Derivative Financial Instruments - Fair Value of Derivative Instruments on the Balance Sheet (Details) - Interest Rate Swap [Member] - Designated as Hedging Instrument [Member] $ in Thousands	Dec. 31, 2017USD ($)
Derivatives, Fair Value [Line Items]
Liability Derivatives, Fair Value	$ 67
Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Fair Value	$ 67

Derivative Financial Instrume80

Derivative Financial Instruments - Effect of Cash Flow Hedging on AOCI (Details) - Cash Flow Hedging [Member] - Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Amount of Loss Recognized in OCI on Derivative	$ 74
Interest Rate Contract [Member]
Derivative [Line Items]
Amount of Loss Recognized in OCI on Derivative	74
Interest Rate Swap [Member]
Derivative [Line Items]
Amount of Loss Recognized in OCI on Derivative	0
Interest Expense [Member]
Derivative [Line Items]
Amount of Loss Reclassified from OCI into Income	176	$ 168
Interest Expense [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Amount of Loss Reclassified from OCI into Income	7	0
Interest Expense [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Amount of Loss Reclassified from OCI into Income	$ 169	$ 168

Stockholders' Equity - Common s

Stockholders' Equity - Common shares (Details) - shares	Aug. 14, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of the beginning and ending common stock outstanding
Balance, beginning of year (shares)		116,417,000
Balance, end of year (shares)		125,132,000	116,417,000
Common Stock [Member]
Reconciliation of the beginning and ending common stock outstanding
Balance, beginning of year (shares)		116,416,900	101,517,009	98,828,098
Issuance of common stock (shares)	8,337,500	8,395,607	14,063,100	2,493,171
Non-vested stock-based awards, net of withheld shares and forfeitures (shares)		319,086	836,791	195,740
Balance, end of year (shares)		125,131,593	116,416,900	101,517,009

Stockholders' Equity - Narrativ

Stockholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	Feb. 13, 2018	Aug. 14, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	May 02, 2017	May 01, 2017
Class of Stock [Line Items]
Common stock, par value (in dollars per share)		$ 0.01	$ 0.01				$ 0.01	$ 0.01
Dividend per share to common stockholders, paid (in dollars per share)				$ 0.3	$ 0.3	$ 0.3	1.20	$ 1.20	$ 1.20
Dividends per share to common stockholders, declared (in dollars per share)			$ 0.30				$ 1.20
Common stock, authorized shares			300,000,000				300,000,000	150,000,000		300,000,000	150,000,000
Number of common shares authorized to be repurchased (shares)			3,000,000				3,000,000
Dividend Declared [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Dividends per share to common stockholders, declared (in dollars per share)	$ 0.30
Common Stock [Member]
Class of Stock [Line Items]
Issuance of common stock (shares)		8,337,500					8,395,607	14,063,100	2,493,171
Price per share (dollars per share)		$ 30.90
Proceeds from Issuance or Sale of Equity		$ 247.1

Stockholders' Equity - At the M

Stockholders' Equity - At the Market Equity Offering Program (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares	Feb. 14, 2018shares	Feb. 19, 2016investment_bankshares	Feb. 17, 2016investment_bank
Class of Stock [Line Items]
Proceeds from Issuance of Common Stock | $	$ 248,554	$ 450,503	$ 66,942
At The Market Equity Offering Program [Member]
Class of Stock [Line Items]
Equity offering program, number of investment banks in sales agreements | investment_bank					5
Equity offering program, shares authorized to be sold					10,000,000
Issuance of common stock (shares)	0	4,795,601	2,434,239
Proceeds from Issuance of Common Stock | $	$ 0	$ 144,600	$ 65,800
Previous At the Market Equity Offering Program [Member]
Class of Stock [Line Items]
Equity offering program, number of investment banks in sales agreements | investment_bank						1
Minimum [Member] | At The Market Equity Offering Program [Member]
Class of Stock [Line Items]
Shares issued during period (USD per share) | $ / shares	$ 0	$ 28.31	$ 25
Maximum [Member] | At The Market Equity Offering Program [Member]
Class of Stock [Line Items]
Shares issued during period (USD per share) | $ / shares	$ 0	$ 33.66	$ 29.15
Subsequent Event [Member] | At The Market Equity Offering Program [Member]
Class of Stock [Line Items]
Number of authorized shares remaining under offering program (shares)				5,868,697

Stockholders' Equity - Accumula

Stockholders' Equity - Accumulated Other Comprehensive Income (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)swap_agreement	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Number of interest rate swaps | swap_agreement	2
Increase to accumulated other comprehensive loss	$ (74)		$ (1,684)
Period of impact on net income	10 years
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income	$ 102	$ 168	$ 950
Forward Starting Swaps [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(1,401)
Other comprehensive loss before reclassifications	176
Amounts reclassified from accumulated other comprehensive income (loss)	(74)
Other comprehensive income	102
Balance, end of period	(1,299)	(1,401)
Interest Rate Swap [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Increase to accumulated other comprehensive loss	100
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	1,400
Balance, end of period	$ 1,300	$ 1,400

Stockholders' Equity - Reclassi

Stockholders' Equity - Reclassifications out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	$ 56,402	$ 57,351	$ 65,534
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	176
Amounts reclassified from accumulated other comprehensive income (loss) related to settled interest rate swaps [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	169
Amounts reclassified from accumulated other comprehensive income (loss) related to current interest rate swaps [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	$ 7

Benefit Plans (Details Textual)

Benefit Plans (Details Textual)	May 05, 2015USD ($)plan_participant	May 31, 2016USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	May 06, 2016USD ($)
Defined Benefit Plan Disclosure [Line Items]
Current period charge	$ 5,300,000
Total benefit obligation	$ 19,600,000		$ 0	$ 0	$ 19,600,000
Number of plan participants who have not reached age 65 | plan_participant	2
Chief Executive Officer [Member]
Defined Benefit Plan Disclosure [Line Items]
Lump sum obligation at termination of plan		$ 14,400,000
Accumulated Other Comprehensive Income (Loss) [Member]
Defined Benefit Plan Disclosure [Line Items]
Current period charge	$ 2,500,000

Benefit Plans (Details)

Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net periodic benefit cost for both the Executive Retirement Plan and the Outside Director Plan
Service cost			$ 29
Interest cost			225
Amortization of prior service cost (benefit)			(198)
Amortization of net gain			343
Total			399
Net loss recognized in Accumulated other comprehensive income (loss)	$ 0	$ 0	0
Total recognized in net periodic benefit gain and Accumulated other comprehensive income (1)			$ 399

Stock and Other Incentive Pla88

Stock and Other Incentive Plans - Amortization of Compensation for Nonvested Shares (Details) $ in Millions	Dec. 31, 2017USD ($)
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
2,018	$ 9.4
2,019	7
2,020	6.7
2,021	5.7
2,022	3.2
2023 and thereafter	3.6
Total	$ 35.6

Stock and Other Incentive Pla89

Stock and Other Incentive Plans (Details) - Stock Incentive Plan [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of the activity under the incentive plans
Stock-based awards, beginning of year (shares)	1,786,497	1,092,262	1,057,732
Granted (shares)	413,489	885,219	251,789
Vested (shares)	(292,341)	(190,984)	(210,955)
Forfeited (shares)	0	0	(6,304)
Stock-based awards, end of year (shares)	1,907,645	1,786,497	1,092,262
Weighted-average grant date fair value of:
Stock-based awards, beginning of year (in USD per share)	$ 27.18	$ 24.72	$ 24.01
Stock-based awards granted during the year (in USD per share)	32.05	29.60	27.70
Stock-based awards vested during the year (in USD per share)	25.88	24.34	25.05
Stock-based awards forfeited during the year (in USD per share)	0	0	24.80
Stock-based awards, end of year (in USD per share)	$ 28.44	$ 27.18	$ 24.72
Grant date fair value of shares granted during the year	$ 13,254	$ 26,204	$ 6,975

Stock and Other Incentive Pla90

Stock and Other Incentive Plans (Details 1) - Employee Stock Purchase Plan [Member] - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock Options Outstanding:
Options outstanding, beginning of year (shares)	316,321	340,958	393,902
Granted (shares)	206,824	198,450	197,640
Exercised (shares)	(32,076)	(57,924)	(44,462)
Forfeited (shares)	(40,659)	(22,081)	(47,176)
Expired (shares)	(132,310)	(143,082)	(158,946)
Outstanding, end of period (shares)	318,100	316,321	340,958
Exercisable, end of period (shares)	318,100	316,321	340,958
Weighted-average exercise price:
Options outstanding, beginning of year (in USD per share)	$ 23.69	$ 20.70	$ 19.17
Options granted during the year (in USD per share)	25.77	24.07	23.22
Options exercised during the year (in USD per share)	24.31	21.40	19.41
Options forfeited during the year (in USD per share)	25.01	23.16	19.90
Options expired during the year (in USD per share)	23.22	18.11	20.41
Options outstanding, end of year (in USD per share)	25	23.69	20.70
Weighted-average fair value of options granted during the year (calculated as of the grant date) (in USD per share)	$ 6.31	$ 5.37	$ 5.39
Intrinsic value of options exercised during the year	$ 271,000	$ 634,000	$ 381,000
Intrinsic value of options outstanding (calculated as of December 31)	2,683,000	2,098,000	2,597,000
Intrinsic value of options exercisable (calculated as of December 31)	$ 2,682,519	$ 2,097,898	$ 2,597,238
Exercise prices of options outstanding (calculated as of December 31) (in USD per share)	$ 25	$ 23.69	$ 20.70
Weighted-average contractual life of outstanding options (calculated as of December 31, in years)	9 months 18 days	9 months 18 days	9 months 18 days

Stock and Other Incentive Pla91

Stock and Other Incentive Plans (Details 2)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair value of options issued based on weighted-average assumptions
Risk-free interest rates	1.20%	1.06%	0.67%
Expected dividend yields	3.70%	4.64%	4.79%
Expected life (in years)	1 year 5 months 12 days	1 year 5 months 1 day	1 year 4 months 17 days
Expected volatility	20.40%	17.60%	21.00%
Expected forfeiture rates	85.00%	85.00%	80.00%

Stock and Other Incentive Pla92

Stock and Other Incentive Plans (Details Textual)

Dec. 11, 2017USD ($)executive_officershares

Dec. 30, 2016USD ($)shares

Dec. 16, 2016USD ($)executive_officershares

Mar. 01, 2016USD ($)shares

Feb. 16, 2016USD ($)executive_officershares

Dec. 18, 2015USD ($)executive_officershares

Jul. 31, 2012

Mar. 31, 2017USD ($)executive_officershares

Mar. 31, 2016USD ($)executive_officershares

Dec. 31, 2022USD ($)

Dec. 31, 2021USD ($)

Dec. 31, 2020USD ($)

Dec. 31, 2019USD ($)

Dec. 31, 2018USD ($)

Dec. 31, 2017USD ($)shares

Dec. 31, 2016USD ($)Awardsshares

Dec. 31, 2015USD ($)shares

Dec. 31, 2014

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Executive Incentive Plan, Cash-based Award

$ 1,100,000

401(k) Plan [Abstract]

Percentage of matching contribution

3.00%

Value of matching contribution

$ 400,000

$ 400,000

$ 400,000

Discount on market price on the date of grant

85.00%

Discount on market price on the date of exercise

85.00%

Employee Stock Purchase Plan [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of shares authorized | shares

25,535

63,690

96,977

401(k) Plan [Abstract]

Value of shares available for grant each year

$ 25,000

Discount on market price on the date of grant

85.00%

Discount on market price on the date of exercise

85.00%

Option expiration period

27 months

Cash received from employees upon exercising options

$ 800,000

$ 1,200,000

$ 900,000

2015 Incentive Plan [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Authorization of common shares to issue | shares

3,500,000

Common shares issued, net of forfeitures | shares

1,438,228

1,024,739

Number of shares authorized | shares

2,061,772

2,475,261

2015 Incentive Plan [Member] | Restricted Stock [Member] | Minimum [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

3 years

2015 Incentive Plan [Member] | Restricted Stock [Member] | Maximum [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

8 years

Stock Incentive Plan [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Common shares issued, net of forfeitures | shares

1,878,637

Granted in period (in shares) | shares

413,489

885,219

251,789

Stock Incentive Plan [Member] | Executive Officer [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based compensation expense

$ 1,700,000

$ 100,000

Number of one-time non-vested share grants | Awards

3

Stock Incentive Plan [Member] | Director [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

1 year

3 years

Share-based compensation expense

$ 800,000

$ 1,000,000

$ 1,000,000

Shares issued under the plan | shares

23,231

21,374

23,201

Stock Incentive Plan [Member] | Chief Financial Officer [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

10 years

Share-based compensation expense

$ 200,000

Granted in period (in shares) | shares

50,000

Stock Incentive Plan [Member] | President and Chief Executive Officer [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

10 years

Share-based compensation expense

$ 600,000

Granted in period (in shares) | shares

200,000

Stock Incentive Plan [Member] | Executive Chairman [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

5 years

Share-based compensation expense

$ 900,000

Granted in period (in shares) | shares

150,000

Stock Incentive Plan [Member] | Restricted Stock [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based compensation expense

$ 9,800,000

$ 7,400,000

$ 5,900,000

Withheld of common stock | shares

94,403

48,248

49,225

Stock Incentive Plan [Member] | Performance Shares [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Value of performance based awards released

$ 1,300,000

$ 1,300,000

Shares issued under the plan | shares

41,368

44,162

Stock Incentive Plan [Member] | Performance Shares [Member] | Executive Officer [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of executive officers granted awards | executive_officer

5

5

Stock Incentive Plan [Member] | Performance Shares [Member] | Senior Vice President [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of executive officers granted awards | executive_officer

4

4

Stock Incentive Plan [Member] | Performance Shares [Member] | Officer [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based compensation expense

$ 1,100,000

$ 0

$ 1,100,000

Stock Incentive Plan [Member] | Performance Shares [Member] | Minimum [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

3 years

Stock Incentive Plan [Member] | Performance Shares [Member] | Maximum [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

8 years

Stock Incentive Plan [Member] | Performance Shares [Member] | Weighted Average [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

6 years

Stock Incentive Plan [Member] | Restricted Stock and Performance Based Awards [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Weighted average amortization period remaining

5 years 1 month 6 days

Stock Incentive Plan [Member] | Restricted Stock and Performance Based Awards [Member] | Minimum [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

1 year

Stock Incentive Plan [Member] | Restricted Stock and Performance Based Awards [Member] | Maximum [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

8 years

Executive Incentive Plan [Member] | Performance Shares [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based compensation expense

$ 5,000,000

4,000,000

2,700,000

Executive Incentive Plan [Member] | Performance Shares [Member] | Minimum [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Shareholder return performance period used to measure award

1 year

Executive Incentive Plan [Member] | Performance Shares [Member] | Maximum [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Shareholder return performance period used to measure award

3 years

Executive Incentive Plan [Member] | 2017 Performance Shares [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

5 years

Granted in period

$ 10,100,000

Granted in period (in shares) | shares

309,874

Executive Incentive Plan [Member] | 2017 Performance Shares [Member] | Executive Officer [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of executive officers granted awards | executive_officer

5

Executive Incentive Plan [Member] | 2017 Performance Shares [Member] | Senior Vice President [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of executive officers granted awards | executive_officer

4

Executive Incentive Plan [Member] | February 2016 Cash Incentive and Performance-based Awards [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Granted in period

$ 5,800,000

Executive Incentive Plan [Member] | February 2016 Cash Incentive and Performance-based Awards [Member] | Executive Officer [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of executive officers granted awards | executive_officer

5

Executive Incentive Plan [Member] | February 2016 Cash Incentive and Performance-based Awards [Member] | Senior Vice President [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of executive officers granted awards | executive_officer

5

Executive Incentive Plan [Member] | February 2016 Performance Shares [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Granted in period

$ 4,700,000

Granted in period (in shares) | shares

163,788

Executive Incentive Plan [Member] | 2015 Performance Shares [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

3 years

Granted in period

$ 3,900,000

Granted in period (in shares) | shares

139,000

Executive Incentive Plan [Member] | 2015 Performance Shares [Member] | Executive Officer [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of executive officers granted awards | executive_officer

5

Executive Incentive Plan [Member] | 2015 Performance Shares [Member] | Senior Vice President [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of executive officers granted awards | executive_officer

5

Executive Incentive Plan [Member] | 2016 Performance Shares [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

5 years

Granted in period

$ 6,300,000

Granted in period (in shares) | shares

213,639

Executive Incentive Plan [Member] | 2016 Performance Shares [Member] | Executive Officer [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of executive officers granted awards | executive_officer

5

Executive Incentive Plan [Member] | 2016 Performance Shares [Member] | Senior Vice President [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of executive officers granted awards | executive_officer

5

Salary Deferral Plan [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based compensation expense

$ 1,200,000

$ 1,200,000

$ 1,100,000

Shares issued under the plan | shares

39,016

42,256

55,923

Maximum salary deferral for officers under the plan, percent

50.00%

Dividend Reinvestment Plan [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Authorization of common shares to issue | shares

1,000,000

401(k) Plan [Abstract]

Total DRIP shares issued under the Plan | shares

581,627

Total shares issued under the Dividend Reinvestment Plan | shares

26,031

9,575

13,950

3-year Vesting [Member] | Executive Incentive Plan [Member] | February 2016 Performance Shares [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

3 years

5-year Vesting [Member] | Executive Incentive Plan [Member] | February 2016 Performance Shares [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

5 years

Deferral Option One [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Salary Deferral Plan employer matching contribution, percent

30.00%

Deferral Option One [Member] | Salary Deferral Plan [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

3 years

Deferral Option Two [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Salary Deferral Plan employer matching contribution, percent

50.00%

Deferral Option Two [Member] | Salary Deferral Plan [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

5 years

Deferral Option Three [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Salary Deferral Plan employer matching contribution, percent

100.00%

Deferral Option Three [Member] | Salary Deferral Plan [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

8 years

Scenario, Forecast [Member] | Executive Incentive Plan [Member] | 2017 Performance Shares [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based compensation expense

$ 1,900,000

$ 2,000,000

$ 2,000,000

$ 2,000,000

$ 2,000,000

Scenario, Forecast [Member] | Executive Incentive Plan [Member] | February 2016 Performance Shares [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based compensation expense

700,000

700,000

1,100,000

Scenario, Forecast [Member] | Executive Incentive Plan [Member] | 2015 Performance Shares [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based compensation expense

1,300,000

Scenario, Forecast [Member] | Executive Incentive Plan [Member] | 2016 Performance Shares [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based compensation expense

$ 1,200,000

$ 1,300,000

$ 1,300,000

$ 1,300,000

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Weighted Average Common Shares
Weighted average Common Shares outstanding									119,739,216	109,861,580	100,280,059
Non-vested shares									(1,813,058)	(1,289,478)	(1,108,707)
Weighted average Common Shares - Basic									117,926,158	108,572,102	99,171,352
Dilutive effect of non-vested shares									0	709,559	623,212
Dilutive effect of employee stock purchase plan									91,007	105,336	85,738
Weighted average Common Shares - Diluted									118,017,165	109,386,997	99,880,302
Net Income
Income (loss) from continuing operations	$ (37,151)	$ 3,165	$ 25,224	$ 31,858	$ 52,580	$ 11,857	$ 12,157	$ 9,163	$ 23,096	$ 85,756	$ 58,836
Dividends paid on nonvested share-based awards									(2,149)	0	0
Income from continuing operations applicable to common stockholders									20,947	85,756	58,836
Discontinued operations	0	8	0	(13)	(143)	(23)	(12)	(7)	(4)	(185)	10,600
NET INCOME	$ (37,151)	$ 3,173	$ 25,224	$ 31,845	$ 52,437	$ 11,834	$ 12,145	$ 9,156	$ 20,943	$ 85,571	$ 69,436
Basic Earnings (loss) Per Common Share
Income from continuing operations (in dollars per share)									$ 0.18	$ 0.79	$ 0.59
Income from discontinued operations (in dollars per share)									0	0	0.11
Net income (in dollars per share)	$ (0.31)	$ 0.02	$ 0.22	$ 0.28	$ 0.46	$ 0.10	$ 0.12	$ 0.09	0.18	0.79	0.70
Diluted Earnings (loss) Per Common Share
Income from continuing operations (in dollars per share)									0.18	0.78	0.59
Income from discontinued operations (in dollars per share)									0	0	0.11
Net income (in dollars per share)	$ (0.31)	$ 0.02	$ 0.22	$ 0.28	$ 0.45	$ 0.10	$ 0.12	$ 0.09	$ 0.18	$ 0.78	$ 0.70

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)ft²land_parcelpropertyrenewal_optionLease	Dec. 31, 2016USD ($)land_parcel	Dec. 31, 2015USD ($)
Property, Plant and Equipment [Line Items]
Approximate square feet | ft²	14,600,000
Number of land parcels held for development | land_parcel	6	6
Investment in land held for development	$ 20,100	$ 20,100
Number of ground leases | property	109
Square feet subject to ground leases | ft²	8,900,000
Ground leases, weighted average remaining term	68 years 8 months 12 days
Approximately corporate office lease covers of rented space | ft²	36,653
Rental expense relating to the operating leases	$ 6,300	5,700	$ 5,100
Number of ground leases prepaid | Lease	48
Prepaid ground leases which represented rental expense	$ 500	$ 500	$ 500
Number of ground leases, excluding prepaid leases | Lease	61
First and Second Generation Leases [Member] | Tenant Improvement Allowances [Member]
Property, Plant and Equipment [Line Items]
Anticipated amount of investment	$ 27,800
Tennessee [Member]
Property, Plant and Equipment [Line Items]
Number of redevelopment properties under expansion | property	1
Total amount funded	$ 12,600
Tennessee [Member] | Tenant Improvement Allowances [Member]
Property, Plant and Equipment [Line Items]
Total amount funded	$ 3,200
Medical Office Building Expansion [Member] | North Carolina [Member]
Property, Plant and Equipment [Line Items]
Approximate square feet | ft²	38,000
Medical Office Building [Member]
Property, Plant and Equipment [Line Items]
Total amount funded	$ 5,759
Estimated total investment	76,120
Estimated remaining fundings (unaudited)	$ 70,361
Approximate square feet | ft²	355,000
Total Funded During the Year	$ 5,073
Medical Office Building [Member] | North Carolina [Member]
Property, Plant and Equipment [Line Items]
Total amount funded	3,487
Estimated total investment	12,000
Estimated remaining fundings (unaudited)	$ 8,513
Approximate square feet | ft²	204,000
Total Funded During the Year	$ 3,264
Medical Office Building [Member] | Washington [Member]
Property, Plant and Equipment [Line Items]
Total amount funded	2,272
Estimated total investment	64,120
Estimated remaining fundings (unaudited)	$ 61,848
Approximate square feet | ft²	151,000
Total Funded During the Year	$ 1,809
Medical Office Building [Member] | Colorado [Member]
Property, Plant and Equipment [Line Items]
Total amount funded	$ 14,600
Approximate square feet | ft²	99,957
Medical Office Building [Member] | Colorado [Member] | Tenant Improvement Allowances [Member]
Property, Plant and Equipment [Line Items]
Total amount funded	$ 2,800
Minimum [Member]
Property, Plant and Equipment [Line Items]
Ground leases, initial term	50 years
Ground leases, number of renewal options | renewal_option	1
Ground leases, renewal term	75 years
Maximum [Member]
Property, Plant and Equipment [Line Items]
Ground leases, initial term	75 years
Ground leases, number of renewal options | renewal_option	2
Ground leases, renewal term	100 years

Commitments and Contingencies95

Commitments and Contingencies - Construction Activity (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)ft²property
Other Commitments [Line Items]
Number of Properties | property	201
Approximate Square Feet | ft²	14,600,000
Medical Office Building [Member]
Other Commitments [Line Items]
Construction in Progress Balance	$ 5,458
Total Funded During the Year	5,073
Total Amount Funded	5,759
Estimated Remaining Fundings (unaudited)	70,361
Estimated Total Investment (unaudited)	$ 76,120
Approximate Square Feet | ft²	355,000
North Carolina [Member] | Medical Office Building [Member]
Other Commitments [Line Items]
Number of Properties | property	1
Construction in Progress Balance	$ 3,487
Total Funded During the Year	3,264
Total Amount Funded	3,487
Estimated Remaining Fundings (unaudited)	8,513
Estimated Total Investment (unaudited)	$ 12,000
Approximate Square Feet | ft²	204,000
Washington [Member] | Medical Office Building [Member]
Other Commitments [Line Items]
Number of Properties | property	1
Construction in Progress Balance	$ 1,971
Total Funded During the Year	1,809
Total Amount Funded	2,272
Estimated Remaining Fundings (unaudited)	61,848
Estimated Total Investment (unaudited)	$ 64,120
Approximate Square Feet | ft²	151,000

Commitments and Contingencies96

Commitments and Contingencies - Minimum lease payments (Details) $ in Thousands	Dec. 31, 2017USD ($)
Future minimum lease payments due to the Company under property operating agreements
2,018	$ 5,341
2,019	5,420
2,020	5,459
2,021	5,488
2,022	5,516
2023 and thereafter	283,056
Total	$ 310,280

Other Data (Details)

Other Data (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Net income	$ 23,092	$ 85,571	$ 69,436
Reconciling items to taxable income:
Depreciation and amortization	46,426	38,260	30,457
Gain or loss on disposition of depreciable assets	1,570	(32,103)	1,659
Impairments	0	121	687
Straight-line rent	(4,551)	(7,101)	(8,833)
Receivable allowances	1,680	2,067	571
Stock-based compensation	1,855	1,301	7,518
Other	6,552	2,236	4,304
Reconciling items to taxable income, total	53,532	4,781	36,363
Taxable income	76,624	90,352	105,799
Dividends paid	$ 142,327	$ 131,759	$ 120,266

Other Data (Details 1)

Other Data (Details 1) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Characterization of distributions on common stock
Ordinary income per share	$ 0.42	$ 0.78	$ 0.61
Return of capital per share	0.50	0.35	0.08
Unrecaptured section 1250 gain per share	0.28	0.07	0.51
Common stock distributions per share	$ 1.2	$ 1.2	$ 1.2
Ordinary income in percent of common stock distribution	34.50%	65.00%	51.00%
Return of capital in percent of common stock distribution	42.00%	29.50%	6.70%
Unrecaptured section 1250 gain in percent of common stock distribution	23.50%	5.50%	42.30%
Common stock distribution in percentage	100.00%	100.00%	100.00%

Other Data (Details 2)

Other Data (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
State income tax expense:
Texas gross margins tax	$ 608	$ 562	$ 528
Other	0	2	37
Total state income tax expense	608	564	565
State income tax payments, net of refunds and collections	$ 555	$ 544	758
Income tax expense in discontinued operations			$ 50

Other Data (Details Textual)

Other Data (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Data (Textual) [Abstract]
Condition to qualify as a REIT as defined under the Internal Revenue Code	Company must meet a number of organizational and operational requirements, including a requirement that it currently distribute at least 90% of its taxable income to its stockholders.
Estimated aggregate total cost of total assets for federal income tax purposes	$ 4,000,000,000	$ 3,700,000,000	$ 3,400,000,000
Number of preferred shares outstanding	0	0	0
Dividends distributed to preferred shares	$ 0

Fair Value of Financial Inst101

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes and bonds payable	$ 1,283.9	$ 1,264.4
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes and bonds payable	$ 1,269.7	$ 1,265.1

Selected Quarterly Financial102

Selected Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of quarterly financial information
Revenues from continuing operations	$ 107,731	$ 106,953	$ 105,245	$ 104,569	$ 105,309	$ 103,659	$ 102,642	$ 100,021	$ 424,499	$ 411,630	$ 388,471
Income (loss) from continuing operations	(37,151)	3,165	25,224	31,858	52,580	11,857	12,157	9,163	23,096	85,756	58,836
Income (loss) from discontinued operations	0	8	0	(13)	(143)	(23)	(12)	(7)	(4)	(185)	10,600
NET INCOME	$ (37,151)	$ 3,173	$ 25,224	$ 31,845	$ 52,437	$ 11,834	$ 12,145	$ 9,156	$ 20,943	$ 85,571	$ 69,436
Net income attributable to common stockholders per share:
Basic earnings per common share (dollars per share)	$ (0.31)	$ 0.02	$ 0.22	$ 0.28	$ 0.46	$ 0.10	$ 0.12	$ 0.09	$ 0.18	$ 0.79	$ 0.70
Diluted earnings per common share (dollars per share)	$ (0.31)	$ 0.02	$ 0.22	$ 0.28	$ 0.45	$ 0.10	$ 0.12	$ 0.09	$ 0.18	$ 0.78	$ 0.70

Selected Quarterly Financial103

Selected Quarterly Financial Data (unaudited) - Additional information (Details) $ in Thousands	3 Months Ended					12 Months Ended
	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)property	Mar. 31, 2017USD ($)property	Dec. 31, 2016USD ($)property	Dec. 31, 2017USD ($)property	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)property
Quarterly Financial Information Disclosure [Abstract]
Gain on sales of real estate assets			$ 16,100	$ 23,400	$ 41,000	$ 39,519	$ 41,038	$ 56,602
Number of properties sold | property			3	6	6	2		2
Impairment charges		$ 5,100
Loss on extinguishment of debt	$ (45,000)					$ 44,985		$ 27,998

Schedule II - Valuation and 104

Schedule II - Valuation and Qualifying Accounts (Details) - Accounts receivable allowance [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 148	$ 179	$ 465
Charged/(Credited) to Costs and Expenses, Additions and Deductions	159	(21)	(194)
Charged to Other Accounts, Additions and Deductions	0	0	0
Uncollectible Accounts Written-off	51	10	92
Balance at End of Period	$ 256	$ 148	$ 179

Schedule III - Real Estate a105

Schedule III - Real Estate and Accumulated Depreciation (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)propertyProperty	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Summary of real estate properties
Number of Properties | property	201
Buildings, Improvements, Lease Intangibles and CIP (1)
Gross real estate asset, Total	$ 3,907,010	$ 3,633,993	$ 3,382,680	$ 3,271,536
Accumulated depreciation	$ 933,220	$ 843,816	$ 762,996	$ 705,135
Medical office/outpatient [Member]
Summary of real estate properties
Number of Properties | Property	193
State	AL, AZ, CA, CO, DC, FL, GA,  HI, IA, IL, IN,  LA, MD, MI, MN, MO, MS, NC, OH, OK, SC, SD, TN, TX, VA, WA
Land (1)
Initial Investment	$ 190,813
Cost Capitalized Subsequent to Acquisition	3,862
Total	194,675
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	2,823,611
Cost Capitalized Subsequent to Acquisition	502,564
Total	3,326,175
Personal Property	4,193
Gross real estate asset, Total	3,525,043
Accumulated depreciation	835,768
Encumbrances	$ 154,916
Medical office/outpatient [Member] | Minimum [Member]
Buildings, Improvements, Lease Intangibles and CIP (1)
Date Acquired	Jan. 1, 1993
Date Constructed	Jan. 1, 1906
Medical office/outpatient [Member] | Maximum [Member]
Buildings, Improvements, Lease Intangibles and CIP (1)
Date Acquired	Dec. 31, 2017
Date Constructed	Dec. 31, 2015
Inpatient [Member]
Summary of real estate properties
Number of Properties | Property	6
State	CA, CO, MO, PA, TX
Land (1)
Initial Investment	$ 8,179
Cost Capitalized Subsequent to Acquisition	0
Total	8,179
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	255,495
Cost Capitalized Subsequent to Acquisition	9,861
Total	265,356
Personal Property	0
Gross real estate asset, Total	273,535
Accumulated depreciation	66,780
Encumbrances	$ 0
Inpatient [Member] | Minimum [Member]
Buildings, Improvements, Lease Intangibles and CIP (1)
Date Acquired	Jan. 1, 1994
Date Constructed	Jan. 1, 1986
Inpatient [Member] | Maximum [Member]
Buildings, Improvements, Lease Intangibles and CIP (1)
Date Acquired	Dec. 31, 2013
Date Constructed	Dec. 31, 2013
Other [Member]
Summary of real estate properties
Number of Properties | Property	10
State	IA, MI, TN, TX, VA
Land (1)
Initial Investment	$ 2,992
Cost Capitalized Subsequent to Acquisition	73
Total	3,065
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	66,440
Cost Capitalized Subsequent to Acquisition	7,143
Total	73,583
Personal Property	600
Gross real estate asset, Total	77,248
Accumulated depreciation	26,032
Encumbrances	$ 0
Other [Member] | Minimum [Member]
Buildings, Improvements, Lease Intangibles and CIP (1)
Date Acquired	Jan. 1, 1993
Date Constructed	Jan. 1, 1964
Other [Member] | Maximum [Member]
Buildings, Improvements, Lease Intangibles and CIP (1)
Date Acquired	Dec. 31, 2015
Date Constructed	Dec. 31, 2015
Real Estate [Member]
Summary of real estate properties
Number of Properties | Property	209
Land (1)
Initial Investment	$ 201,984
Cost Capitalized Subsequent to Acquisition	3,935
Total	205,919
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	3,145,546
Cost Capitalized Subsequent to Acquisition	519,568
Total	3,665,114
Personal Property	4,793
Gross real estate asset, Total	3,875,826
Accumulated depreciation	928,580
Encumbrances	$ 154,916
Land Held for Development [Member]
Summary of real estate properties
Number of Properties | Property	0
Land (1)
Initial Investment	$ 20,123
Cost Capitalized Subsequent to Acquisition	0
Total	20,123
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	0
Cost Capitalized Subsequent to Acquisition	0
Total	0
Personal Property	0
Gross real estate asset, Total	20,123
Accumulated depreciation	239
Encumbrances	0
Construction in Progress [Member]
Buildings, Improvements, Lease Intangibles and CIP (1)
Total	5,458
Gross real estate asset, Total	$ 5,458
Corporate Property [Member]
Summary of real estate properties
Number of Properties | Property	0
Land (1)
Initial Investment	$ 0
Cost Capitalized Subsequent to Acquisition	0
Total	0
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	0
Cost Capitalized Subsequent to Acquisition	0
Total	0
Personal Property	5,603
Gross real estate asset, Total	5,603
Accumulated depreciation	4,401
Encumbrances	$ 0
Owned Property [Member]
Summary of real estate properties
Number of Properties | Property	209
Land (1)
Initial Investment	$ 222,107
Cost Capitalized Subsequent to Acquisition	3,935
Total	226,042
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	3,145,546
Cost Capitalized Subsequent to Acquisition	519,568
Total	3,670,572
Personal Property	10,396
Gross real estate asset, Total	3,907,010
Accumulated depreciation	933,220
Encumbrances	$ 154,916

Schedule III - Real Estate a106

Schedule III - Real Estate and Accumulated Depreciation (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Beginning Balance, Total Property	$ 3,633,993	$ 3,382,680	$ 3,271,536
Retirement/dispositions:
Ending Balance, Total Property	3,907,010	3,633,993	3,382,680
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Beginning Balance, Accumulated Depreciation	843,816	762,996	705,135
Retirement/dispositions:
Ending Balance, Accumulated Depreciation	933,220	843,816	762,996
Real Estate [Member]
Additions during the period:
Total Property	322,616	239,265	183,478
Retirement/dispositions:
Total Property	(123,639)	(94,143)	(139,741)
Ending Balance, Total Property	3,875,826
Additions during the period:
Accumulated Depreciation	4,206	3,898	3,048
Retirement/dispositions:
Accumulated Depreciation	(50,683)	(44,696)	(56,838)
Ending Balance, Accumulated Depreciation	928,580
Other improvements [Member]
Additions during the period:
Total Property	59,442	70,595	47,985
Additions during the period:
Accumulated Depreciation	135,807	121,592	111,625
Land held for development [Member]
Additions during the period:
Total Property	0	0	500
Retirement/dispositions:
Total Property	0	0	(102)
Additions during the period:
Accumulated Depreciation	74	26	26
Retirement/dispositions:
Accumulated Depreciation	0	0	0
Construction in Progress [Member]
Additions during the period:
Total Property	14,598	35,596	19,024
Retirement/dispositions:
Ending Balance, Total Property	5,458
Additions during the period:
Accumulated Depreciation	$ 0	$ 0	$ 0

Schedule III - Real Estate a107

Schedule III - Real Estate and Accumulated Depreciation (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)property	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Number of real estate assets held for sale | property	8
Gross value of assets held for sale	$ 68,400
Accumulated depreciation on real estate assets held for sale	35,800
Issuance costs	7,488
Estimated aggregate total cost of total assets for federal income tax purposes	$ 4,000,000	$ 3,700,000	$ 3,400,000
Minimum [Member] | Building and improvements [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Asset estimated useful life	3 years 3 months 18 days
Minimum [Member] | Lease intangibles [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Asset estimated useful life	2 years 1 month 6 days
Minimum [Member] | Personal Property [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Asset estimated useful life	2 years 9 months 18 days
Minimum [Member] | Land improvements [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Asset estimated useful life	5 years
Maximum [Member] | Building and improvements [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Asset estimated useful life	39 years
Maximum [Member] | Lease intangibles [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Asset estimated useful life	99 years 6 days
Maximum [Member] | Personal Property [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Asset estimated useful life	20 years
Maximum [Member] | Land improvements [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Asset estimated useful life	39 years
Mortgage Notes [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Issuance costs	$ 900
Mortgage notes payable [Member] | Mortgage Notes [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Unamortized premium	2,651	2,569
Unaccreted discount	1,332	1,450
Issuance costs	$ 853	$ 436

Schedule IV - Mortgage Loans108

Schedule IV - Mortgage Loans on Real Estate (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Rollforward of Mortgage loans on real estate
Balance at beginning of period	$ 0	$ 0	$ 1,900
Deductions during period:
Principal repayments and reductions	0	0	(1,900)
Deductions during period, total	0	0	(1,900)
Balance at end of period	$ 0	$ 0	$ 0