Schedule III: Rollforward of Real Estate Assets and Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of carrying amount of real estate investments rollforward
Balance at beginning of period	$ 1,029,472	$ 993,927	$ 919,576
Subtotal real estate	1,035,230	1,040,662	993,984
Less: Fully depreciated assets	(1,679)	(11,190)	(57)
Balance at end of the period	1,033,551	1,029,472	993,927
Reconciliation of Real Estate Accumulated Depreciation
Balance at beginning of period	225,533	210,025	185,375
Additions charged to operating expenses	28,883	26,698	24,707
Subtotal of accumulated depreciation	254,416	236,723	210,082
Less: Fully depreciated assets	(1,679)	(11,190)	(57)
Balance at end of the period	252,737	225,533	210,025
Land
Reconciliation of carrying amount of real estate investments rollforward
Real Estate, Improvements	0	0	0
Buildings and leasehold improvements
Reconciliation of carrying amount of real estate investments rollforward
Real Estate, Improvements	12,464	112,538	4,043
Development and construction in progress
Reconciliation of carrying amount of real estate investments rollforward
Real Estate, Improvements	$ (6,706)	$ (65,803)	$ 70,365