Summary of Significant Accounting Policies - Impact of Adoption of New Accounting Standard (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Rental income	$ 109,566	$ 103,384	$ 219,795	$ 206,093
Other operating	2,068	1,934	3,963	3,869
Revenues	111,634	105,318	223,758	209,962
Interest and other income, net	38	4	530	41
NET INCOME	$ 37,729	25,224	$ 46,908	57,070
As Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Rental income		104,869		208,957
Other operating		376		857
Revenues		105,245		209,814
Interest and other income, net		77		189
NET INCOME		$ 25,224		$ 57,070