Discontinued Operations - Discontinued operations balance sheet components (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Land	$ 83,709	$ 87,235
Buildings and improvements	146,580	147,670
Projects under construction	2,028	1,764
Total investments in properties	232,317	236,669
Less accumulated depreciation and depletion	28,446	26,755
Net investments in properties	203,871	209,914
Accounts receivable, net	648	615
Unrealized rents	595	223
Deferred costs	1,228	2,708
Other assets	178	179
Assets of discontinued operations	2,210	176,694
Secured notes payable, current portion	0	125
Secured notes payable, less current portion	88,720	90,029
Accounts payable and accrued liabilities	3,072	2,081
Deferred revenue	26	107
Federal and state income taxes payable	728	0
Tenant security deposits	47	54
Liabilities of discontinued operations	46,456	32,280
Discontinued Operations, Disposed of by Sale [Member]
Land	546	40,465
Buildings and improvements	3,315	186,657
Projects under construction	0	6,617
Total investments in properties	3,861	233,739
Less accumulated depreciation and depletion	2,331	68,049
Net investments in properties	1,530	165,690
Accounts receivable, net	332	405
Unrealized rents	94	4,088
Deferred costs	251	6,509
Other assets	3	2
Assets of discontinued operations	2,210	176,694
Secured notes payable, current portion	0	23,825
Secured notes payable, less current portion	0	4,338
Accounts payable and accrued liabilities	189	2,289
Deferred revenue	2	967
Federal and state income taxes payable	46,228	0
Tenant security deposits	37	861
Liabilities of discontinued operations	$ 46,456	$ 32,280