Impairment Loss on Real Estate Assets (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2016 USD ($) property	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment loss on real estate assets		$ 0	$ 46,461	$ 33,901
Disposal Group, Held-for-sale, Not Discontinued Operations | 150 West Jefferson
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment loss on real estate assets		0	0	8,259
Disposal Group, Held-for-sale, Not Discontinued Operations | 9200 and 9211 Corporate Boulevard
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment loss on real estate assets		0	0	22,950
Impairment of real estate	$ 23,000
Number of assets sold | property	2
Disposal Group, Held-for-sale, Not Discontinued Operations | Disposal Group of 13 Assets
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment loss on real estate assets		0	46,461	0
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 9221 Corporate Boulevard
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment loss on real estate assets		$ 0	$ 0	2,692
Impairment of real estate				$ 2,700