SCHEDULE III REAL ESTATE AND ACCUMULATED DEPRECIATION - Summary (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Carrying cost
Balance at beginning of period	$ 1,392,122	$ 1,301,563	$ 1,198,686
Acquisitions	40,408	82,405	74,923
Improvements	38,528	25,800	49,134
Capitalized interest	1,248	908	1,408
Other non-cash items (See Note 4)			2,460
Cost of real estate sold	(50,850)	(18,554)	(24,282)
Impairment on real estate for sale			(766)
Ending balance	1,421,456	1,392,122	1,301,563
Accumulated depreciation
Balance at beginning of period	306,033	275,861	251,265
Depreciation expense	37,416	37,492	35,809
Cost of real estate sold	(28,574)	(7,320)	(11,213)
Ending balance	$ 314,875	$ 306,033	$ 275,861