SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION - Property Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Real Estate Assets
Balance, beginning of period	$ 2,061,372	$ 2,036,794	$ 1,953,848
Additions
Improvements	31,844	31,342	28,879
Property acquisitions	0	11,041	63,528
Asset sales	(61,801)	(6,237)	0
Deductions: retirements	(9,921)	(11,568)	(9,461)
Balance, end of period	2,021,494	2,061,372	2,036,794
Accumulated Depreciation
Balance, beginning of period	(369,661)	(320,857)	(271,683)
Additions: Depreciation	(62,239)	(61,915)	(58,635)
Asset sales	7,427	1,543	0
Deductions: retirements	9,921	11,568	9,461
Balance, end of period	$ (414,552)	$ (369,661)	$ (320,857)