Summary of Significant Accounting Policies - Deferred Costs and Other Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred costs and other assets
Deferred lease costs, net	$ 250,442	$ 250,261
In-place lease intangibles, net	96,054	153,015
Acquired above market lease intangibles, net	92,405	112,024
Marketable securities of our captive insurance companies	55,664	58,142
Goodwill	20,098	20,098
Other marketable and non-marketable securities	275,130	308,591
Prepaids, notes receivable and other assets, net	584,190	451,457
Deferred costs and other assets	1,373,983	1,353,588
Deferred Lease Costs
Deferred lease costs, gross	485,977	464,226
Accumulated amortization	(235,535)	(213,965)
Deferred lease costs, net	250,442	250,261
Amortization, included in statements of operations and comprehensive income
Amortization of deferred leasing costs	$ 54,323	$ 49,993	$ 43,788