Assets Held for Sale and Property Disposition (Details) $ in Thousands	3 Months Ended
	Jun. 30, 2020 USD ($) property	Dec. 31, 2019 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties held for sale | property	0
Accumulated amortization (intangible lease assets)	$ 58,148	$ 50,766
Total other assets held for sale, net	0	28,201
Intangible lease liabilities, less accumulated amortization of $0 and $31,959 as of June 30, 2020 and December 31, 2019, respectively	0	7,657
Intangible lease liabilities, accumulated amortization	21,856	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	191,400
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	139,690
Straight-line rent receivables	0	18,776
Deferred lease costs, less accumulated amortization of $0 and $34,957 as of June 30, 2020 and December 31, 2019, respectively	0	9,425
Accumulated amortization on deferred lease costs	0	34,957
Total other assets held for sale, net	0	28,201
Intangible lease liabilities, less accumulated amortization of $0 and $31,959 as of June 30, 2020 and December 31, 2019, respectively	0	7,657
Intangible lease liabilities, accumulated amortization	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 June 30, 2020 and December 31, 2019, respectively	0	6,574
Accumulated amortization (intangible lease assets)	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	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	112,287
Accumulated depreciation (building improvements)	$ 0	$ 66,823