Selected Quarterly Financial Data - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended					12 Months Ended
	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Loss on asset impairment		$ 18,400	$ 1,300			$ 19,714	$ 58,476	$ 17,162
(Loss) gain on sale of properties	$ (29,200)			$ 82,200	$ 106,400
111 Monument Circle
Schedule of Equity Method Investments [Line Items]
Lease termination fee					$ 16,600