SCHEDULE III Real Estate and Accumulated Depreciation - Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Accumulated Depreciation [Roll Forward]
Balance at beginning of year	$ 883,445	$ 818,323	$ 754,861
Depreciation	67,652	65,122	63,718
Disposals	(1,467)		(256)
Balance at end of year	$ 949,630	$ 883,445	$ 818,323