Schedule III - Real Estate and Accumulated Depreciation (Details 2) - 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 and Accumulated Depreciation [Line Items]
Federal income tax purposes	$ 1,800,000
Real Estate:
Beginning balance	2,501,844	$ 2,255,260	$ 2,214,057
Additions to/improvements of real estate	153,163	255,527	49,685
Assets sold/written-off	(11,942)	(8,943)	(8,482)
Ending balance	2,643,065	2,501,844	2,255,260
Accumulated Depreciation
Beginning balance	492,582	429,814	371,563
Depreciation expense	70,592	65,723	60,856
Assets sold/written-off	(4,517)	(2,955)	(2,605)
Ending balance	$ 558,657	$ 492,582	$ 429,814
Land improvements
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Useful life	7 years
Building
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Useful life	50 years
Buildings and improvements | Minimum
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Useful life	7 years
Buildings and improvements | Maximum
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Useful life	15 years
Leasehold improvements
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Useful life	15 years