Investment in Unconsolidated and Consolidated Joint Ventures Investment in Unconsolidated and Consolidated Joint Ventures - Condensed Statements of Operations and Balance Sheet Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Statement of Operations
Revenues	$ 35,160,000	$ 27,249,000	$ 65,770,000	$ 54,295,000
Earnings(Loss)	2,511,000	3,117,000	2,672,000	5,569,000
Equity in Earnings(Loss)	1,560,000	1,842,000	1,788,000	3,297,000
Balance Sheet Information
Assets	215,466,000		215,466,000		$ 200,109,000
Debt	(104,649,000)		(104,649,000)		(97,318,000)
Equity	104,834,000		104,834,000		99,265,000
Equity	34,505,000		34,505,000		33,803,000
Petro Travel Plaza Holdings LLC
Statement of Operations
Revenues	30,825,000	24,098,000	57,232,000	48,052,000
Earnings(Loss)	3,021,000	2,838,000	4,523,000	5,129,000
Equity in Earnings(Loss)	1,813,000	1,702,000	2,714,000	3,077,000
Balance Sheet Information
Assets	73,894,000		73,894,000		68,652,000
Debt	(15,277,000)		(15,277,000)		(15,275,000)
Equity	55,810,000		55,810,000		51,287,000
Equity	21,086,000		21,086,000		18,372,000
Five West Parcel
Statement of Operations
Revenues	702,000	694,000	1,418,000	1,484,000
Earnings(Loss)	231,000	221,000	500,000	549,000
Equity in Earnings(Loss)	116,000	111,000	250,000	275,000
Balance Sheet Information
Assets	15,849,000		15,849,000		16,614,000
Debt	(9,981,000)		(9,981,000)		(10,251,000)
Equity	5,568,000		5,568,000		6,043,000
Equity	2,600,000		2,600,000		2,837,000
18-19 West LLC
Statement of Operations
Revenues	2,000	2,000	5,000	4,000
Earnings(Loss)	(30,000)	(29,000)	(54,000)	(72,000)
Equity in Earnings(Loss)	(14,000)	(14,000)	(27,000)	(36,000)
Balance Sheet Information
Assets	4,645,000		4,645,000		4,623,000
Debt	0		0		0
Equity	4,638,000		4,638,000		4,621,000
Equity	1,745,000		1,745,000		1,741,000
TRCC/Rock Outlet Center
Statement of Operations
Revenues	2,726,000	2,455,000	5,275,000	4,755,000
Earnings(Loss)	(82,000)	87,000	(1,091,000)	(37,000)
Equity in Earnings(Loss)	(41,000)	43,000	(546,000)	(19,000)
Balance Sheet Information
Assets	84,281,000		84,281,000		86,056,000
Debt	(49,741,000)		(49,741,000)		(50,712,000)
Equity	33,431,000		33,431,000		34,523,000
Equity	8,652,000		8,652,000		9,198,000
TRC-MRC 1 LLC
Statement of Operations
Revenues	0	0	0	0
Earnings(Loss)	0	0	(2,000)	0
Equity in Earnings(Loss)	0	0	(1,000)	0
Balance Sheet Information
Assets	14,533,000		14,533,000		199,000
Debt	(8,570,000)		(8,570,000)		0
Equity	4,542,000		4,542,000		199,000
Equity	0		0		224,000
TRC-MRC 2 LLC
Statement of Operations
Revenues	905,000	0	1,840,000	0
Earnings(Loss)	(629,000)	0	(1,204,000)	0
Equity in Earnings(Loss)	(314,000)	0	(602,000)	0
Balance Sheet Information
Assets	22,264,000		22,264,000		23,965,000
Debt	(21,080,000)		(21,080,000)		(21,080,000)
Equity	845,000		845,000		2,592,000
Equity	422,000		422,000		1,431,000
Centennial
Statement of Operations
Revenues	0	36,000	1,000	72,000
Earnings(Loss)	(207,000)	$ (57,000)	(317,000)	$ (225,000)
Balance Sheet Information
Assets	87,136,000		87,136,000		86,099,000
Debt					0
Equity	$ 86,425,000		$ 86,425,000		$ 85,281,000