Summary of Significant Accounting Policies (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) property vote Joint_Venture $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($)	Jan. 01, 2019 USD ($)
Significant Accounting Policies [Line Items]
Number of real estate properties | property	4
Number of joint ventures | Joint_Venture	3
Interest capitalized	$ 1,400	$ 200	$ 4,600
Intangible Lease Liabilities (Below-Market In-Place Leases)	94,852	95,620
Amortization of Intangible Lease Origination Costs and In-Place Lease Valuation included in amortization expense	48,940	58,467	58,150
Amortization of Above-Market and Below-Market In-Place Lease intangibles as a net increase to rental revenues	7,615	6,575	5,066
Finite-Lived Intangible Assets, Future Amortization Expense [Abstract]
Total	77,676	77,805
Below Market Lease, Net, Amortization Income, Fiscal Maturity [Abstract]
2019	8,273
2020	6,654
2021	6,443
2022	5,878
2023	4,367
Thereafter	4,093
Total	$ 35,708
Weighted-Average Amortization Period (in years)	6 years
Significant Accounting Policies [Abstract]
Provision for doubtful accounts	$ 91	350	216
Capitalized internal leasing costs	300	300	400
Amortization of deferred lease costs	43,600	50,800	50,100
Amortization of lease incentive	2,600	4,800	3,900
Amortization of fair value adjustments	500	500	500
Amortization of debt discount	200	200	200
Amortization of deferred financing costs and fair market value adjustments on notes payable	$ 2,400	$ 2,800	2,900
Shares-in-trust, shares authorized | shares	150,000,000	150,000,000
Preferred stock, shares authorized | shares	100,000,000	100,000,000
Common stock, shares authorized | shares	750,000,000	750,000,000
Common stock, par value (in dollars per share) | $ / shares	$ 0.01	$ 0.01
Number of votes for each share of common stock | vote	1
Stock repurchase program, remaining authorized repurchase amount	$ 86,600
Dividend reinvestment plan, shareholders discount	2.00%
Income tax benefit (expense)	$ 97	$ (13)	(415)
Rental income	411,667	455,125	439,918
General and administrative	29,713	29,319	27,382
Property operating costs	209,338	222,441	220,796
Deferred Compensation, Excluding Share-based Payments and Retirement Benefits
Significant Accounting Policies [Abstract]
Assets held as trading securities	400
Above-Market In-place Lease Assets
Significant Accounting Policies [Line Items]
Intangible lease assets	7,620	11,935
Finite-Lived Intangible Assets, Future Amortization Expense [Abstract]
2019	938
2020	197
2021	141
2022	121
2023	97
Thereafter	64
Total	$ 1,558
Weighted-Average Amortization Period (in years)	3 years
In-Place Lease Valuation
Significant Accounting Policies [Line Items]
Intangible lease assets	$ 157,447	165,015
Finite-Lived Intangible Assets, Future Amortization Expense [Abstract]
2019	20,876
2020	14,540
2021	12,449
2022	10,948
2023	7,370
Thereafter	9,935
Total	$ 76,118
Weighted-Average Amortization Period (in years)	5 years
Intangible Lease Origination Costs
Significant Accounting Policies [Line Items]
Intangible lease assets	$ 241,516	250,539
Finite-Lived Intangible Assets, Future Amortization Expense [Abstract]
2019	29,503
2020	22,570
2021	19,818
2022	17,550
2023	11,774
Thereafter	18,952
Total	$ 120,167
Weighted-Average Amortization Period (in years)	6 years
Building
Significant Accounting Policies [Line Items]
Useful life	40 years
Building improvements | Minimum
Significant Accounting Policies [Line Items]
Useful life	5 years
Building improvements | Maximum
Significant Accounting Policies [Line Items]
Useful life	25 years
Land improvements | Minimum
Significant Accounting Policies [Line Items]
Useful life	20 years
Land improvements | Maximum
Significant Accounting Policies [Line Items]
Useful life	25 years
Furniture, fixtures, and equipment | Minimum
Significant Accounting Policies [Line Items]
Useful life	3 years
Furniture, fixtures, and equipment | Maximum
Significant Accounting Policies [Line Items]
Useful life	5 years
1201 Eye Street NW Associates LLC and 1225 Eye Street, NW Associates LLC
Significant Accounting Policies [Line Items]
Number of real estate properties | property	2
Accounting Standards Update 2016-01
Significant Accounting Policies [Abstract]
Cumulative effect of accounting change	$ (100)
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Significant Accounting Policies [Abstract]
Rental income		(19,200)	(19,000)
Property related revenue		19,200	19,000
General and administrative		(1,800)	(1,900)
Restatement Adjustment
Significant Accounting Policies [Abstract]
Property operating costs		$ 1,800	$ 1,900
Subsequent Event | Accounting Standards Update 2016-02
Significant Accounting Policies [Abstract]
Lease liability				$ 300