Schedule III- Real Estate Assets and Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Real estate:
Balance at the beginning of the period	$ 986,215	$ 718,764	$ 492,486
Acquisitions	280,477	270,601	226,078
Improvements	744	726	230
Sales of real estate	(952)	(3,876)	(30)
Balance at the end of the period	1,266,484	986,215	718,764
Accumulated depreciation:
Balance at the beginning of the period	(121,797)	(97,667)	(78,897)
Depreciation expense	(30,493)	(25,001)	(18,770)
Sales of real estate	105	871	0
Balance at the end of the period	$ (152,185)	$ (121,797)	$ (97,667)