Assets Held for Sale and Property Disposition (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jun. 30, 2020 USD ($)	Sep. 30, 2020 USD ($) property	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) property	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties held for sale | property		0		0
Impairment loss on real estate assets		$ 0	$ 1,953	$ 0	$ 1,953
Accumulated amortization (intangible lease assets)		63,353		63,353		$ 50,766
Total other assets held for sale, net		0		0		28,201
Intangible lease liabilities, less accumulated amortization of $0 and $31,959 as of September 30, 2020 and December 31, 2019, respectively		0		0		7,657
Intangible lease liabilities, accumulated amortization		24,881		24,881		19,607
1901 Market Street
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of property	$ 350,800
Gain on sale of real estate assets	$ 191,000
The Dupree
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment loss on real estate assets					$ 2,000
Disposal Group, Held-for-sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total real estate assets held for sale, net		0		0		139,690
Straight-line rent receivables		0		0		18,776
Deferred lease costs, less accumulated amortization of $0 and $34,957 as of September 30, 2020 and December 31, 2019, respectively		0		0		9,425
Accumulated amortization on deferred lease costs		0		0		34,957
Total other assets held for sale, net		0		0		28,201
Intangible lease liabilities, less accumulated amortization of $0 and $31,959 as of September 30, 2020 and December 31, 2019, respectively		0		0		7,657
Intangible lease liabilities, accumulated amortization		0		0		31,959
Disposal Group, Held-for-sale, Not Discontinued Operations | Intangible lease assets
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Intangible lease assets, less accumulated amortization of $0 and $27,438 as of September 30, 2020 and December 31, 2019, respectively		0		0		6,574
Accumulated amortization (intangible lease assets)		0		0		27,438
Disposal Group, Held-for-sale, Not Discontinued Operations | Land
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate assets held for sale, net		0		0		20,829
Disposal Group, Held-for-sale, Not Discontinued Operations | Building and building improvements
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate assets held for sale, net		0		0		112,287
Accumulated depreciation (building improvements)		$ 0		$ 0		$ 66,823