Deferred Costs (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred leasing costs	$ 443,341	$ 468,971
Less: accumulated amortization	(217,140)	(201,371)
Deferred costs, net	$ 226,201	$ 267,600