UNSECURED AND SECURED DEBT (Tables)

12 Months Ended

Dec. 31, 2017

Debt Instrument [Line Items]

Schedule of long-term debt instruments

	December 31, 2017			December 31, 2016
	(In thousands)
Unsecured bank credit facilities - variable rate, carrying amount	$	116,339		112,020
Unsecured bank credit facilities - fixed rate, carrying amount(1)	80,000			80,000
Unamortized debt issuance costs	(630		)	(1,030	)
Unsecured bank credit facilities	195,709			190,990
Unsecured debt - fixed rate, carrying amount (1)	715,000			655,000
Unamortized debt issuance costs	(1,939		)	(2,162	)
Unsecured debt	713,061			652,838
Secured debt - fixed rate, carrying amount (1)	200,354			258,594
Unamortized debt issuance costs	(842		)	(1,089	)
Secured debt	199,512			257,505
Total debt	$	1,108,282		1,101,333

(1) These loans have a fixed interest rate or an effectively fixed interest rate due to interest rate swaps.

Schedule of unsecured debt [Table Text Block]

A summary of the carrying amount of Unsecured debt follows:

				Balance at December 31,
	Margin Above LIBOR	Interest Rate	Maturity Date	2017		2016
				(In thousands)
$50 Million Unsecured Term Loan	Not applicable	3.910%	12/21/2018	$	50,000	50,000
$75 Million Unsecured Term Loan (1)	1.150%	2.846%	07/31/2019	75,000		75,000
$75 Million Unsecured Term Loan (1)	1.100%	3.452%	12/20/2020	75,000		75,000
$40 Million Unsecured Term Loan (1)	1.100%	2.335%	07/30/2021	40,000		40,000
$75 Million Unsecured Term Loan (1)	1.400%	3.031%	02/28/2022	75,000		75,000
$65 Million Unsecured Term Loan (1)	1.650%	2.863%	04/01/2023	65,000		65,000
$100 Million Senior Unsecured Notes:
$30 Million Notes	Not applicable	3.800%	08/28/2020	30,000		30,000
$50 Million Notes	Not applicable	3.800%	08/28/2023	50,000		50,000
$20 Million Notes	Not applicable	3.800%	08/28/2025	20,000		20,000
$60 Million Senior Unsecured Notes	Not applicable	3.460%	12/13/2024	60,000		—
$100 Million Senior Unsecured Notes:
$60 Million Notes	Not applicable	3.480%	12/15/2024	60,000		60,000
$40 Million Notes	Not applicable	3.750%	12/15/2026	40,000		40,000
$25 Million Senior Unsecured Notes	Not applicable	3.970%	10/01/2025	25,000		25,000
$50 Million Senior Unsecured Notes	Not applicable	3.990%	10/07/2025	50,000		50,000
				$	715,000	655,000

(1) The interest rates on these unsecured term loans are comprised of LIBOR plus a margin which is subject to a pricing grid for changes in the Company's coverage ratings. The Company entered into interest rate swap agreements (further described in Note 13) to convert the loans' LIBOR rates to effectively fixed interest rates. The interest rates in the table above are the effectively fixed interest rates for the loans, including the effects of the interest rate swaps, as of December 31, 2017.

Secured debt

A summary of the carrying amount of Secured debt follows: 

	Interest Rate	Monthly P&I Payment	Maturity Date	Carrying Amount of Securing Real Estate at December 31, 2017		Balance at December 31,
Property						2017	2016
				(In thousands)
Arion 16, Broadway VI, Chino, East University I & II, Northpark, Santan 10 II, 55th Avenue and World Houston 1 & 2, 21 & 23	5.57%	518,885	Repaid	$	—	—	47,496
Dominguez, Industry I & III, Kingsview, Shaw, Walnut and Washington	7.50%	539,747	05/05/2019	45,886		49,580	52,231
Blue Heron II	5.39%	16,176	02/29/2020	4,425		409	576
40th Avenue, Beltway Crossing V, Centennial Park, Executive Airport, Interchange Park I, Ocean View, Wetmore 5-8 and World Houston 26, 28, 29 & 30	4.39%	463,778	01/05/2021	67,796		55,317	58,380
Colorado Crossing, Interstate I-III, Rojas, Steele Creek 1 & 2, Venture and World Houston 3-9	4.75%	420,045	06/05/2021	56,000		50,161	52,752
Arion 18, Beltway Crossing VI & VII, Commerce Park II & III, Concord, Interstate V-VII, Lakeview, Ridge Creek II, Southridge IV & V and World Houston 32	4.09%	329,796	01/05/2022	56,440		42,315	44,493
Ramona	3.85%	16,287	11/30/2026	9,027		2,572	2,666
				$	239,574	200,354	258,594

Principal payments due during the next five years

Principal payments on long-term debt, including Unsecured debt and Secured debt (not including Unsecured bank credit facilities), due during the next five years as of December 31, 2017 are as follows: 

Years Ending December 31,	(In thousands)
2018	$	61,314
2019	130,569
2020	114,096
2021	129,563
2022	107,769