Debt - Mortgage Loans Payable (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Loan bears interest, description of variable rate basis	LIBOR plus 3%
Mortgage loans payable	$ 375,335	$ 444,933
Memphis, TN [Member] | 3.00 Loan Due in Aug 2015 [Member]
Debt Instrument [Line Items]
Maturity	Aug 2015
Loan bears interest, description of variable rate basis	Libor + 2.5 %
Interest Rate	3.00%
Mortgage loans payable	12,908	13,125
Lisle, IL [Member] | 2.66% Loan Due Oct 2015 [Member]
Debt Instrument [Line Items]
Maturity	Oct 2015
Loan bears interest, description of variable rate basis	Libor + 2.5 %
Interest Rate	2.66%
Mortgage loans payable	5,752	5,752
Lisle, IL [Member] | 5.55% Loan Due in Mar 2017 [Member]
Debt Instrument [Line Items]
Maturity	Mar 2017
Loan bears interest, description of variable rate basis	-
Interest Rate	5.55%
Mortgage loans payable	5,411	5,470
Chicago, IL [Member]
Debt Instrument [Line Items]
Maturity	n/a
Loan bears interest, description of variable rate basis	-
Mortgage loans payable		8,579
Chicago, IL [Member] | 5.75% Loan Due in Mar 2016 [Member]
Debt Instrument [Line Items]
Maturity	Mar 2016
Loan bears interest, description of variable rate basis	-
Interest Rate	5.75%
Mortgage loans payable	19,614	19,856
New York, NY [Member] | 3.50% Loan Due in May 2016 [Member]
Debt Instrument [Line Items]
Maturity	May 2016
Loan bears interest, description of variable rate basis	Libor + 2.5 %
Interest Rate	3.50%
Mortgage loans payable	51,298	51,950
Philadelphia, PA [Member] | 2.50% Loan Due in May 2016 [Member]
Debt Instrument [Line Items]
Maturity	May 2016
Loan bears interest, description of variable rate basis	Libor + 2.0 %
Interest Rate	2.50%
Mortgage loans payable	41,705	42,440
Greensboro, North Carolina Sale [Member] | 6.22% Loan Due in Aug 2016 [Member]
Debt Instrument [Line Items]
Maturity	Aug 2016
Loan bears interest, description of variable rate basis	-
Interest Rate	6.22%
Mortgage loans payable	13,600	14,735
Phoenix, AZ [Member] | 2.69% Loan Due in Oct 2016 [Member]
Debt Instrument [Line Items]
Maturity	Oct 2016
Loan bears interest, description of variable rate basis	Libor + 2.0 %
Interest Rate	2.69%
Mortgage loans payable	24,390	24,390
San Pedro, CA [Member] | 2.69% Loan Due in Oct 2016 [Member]
Debt Instrument [Line Items]
Maturity	Oct 2016
Loan bears interest, description of variable rate basis	Libor + 2.0 %
Interest Rate	2.69%
Mortgage loans payable	12,195	12,195
Stamford, CT [Member] | 2.69% Loan Due in Oct 2016 [Member]
Debt Instrument [Line Items]
Maturity	Oct 2016
Loan bears interest, description of variable rate basis	Libor + 2.0 %
Interest Rate	2.69%
Mortgage loans payable	48,780	48,780
Houston, TX [Member]
Debt Instrument [Line Items]
Maturity	Apr 2016
Loan bears interest, description of variable rate basis	-
Mortgage loans payable		47,201
Houston, TX [Member] | 2.69% Loan Due in Oct 2016 [Member]
Debt Instrument [Line Items]
Maturity	Oct 2016
Loan bears interest, description of variable rate basis	Libor + 2.0 %
Interest Rate	2.69%
Mortgage loans payable	64,635	64,635
Cerritos, CA [Member] | 5.07% Loan Due in Jan 2017 [Member]
Debt Instrument [Line Items]
Maturity	Jan 2017
Loan bears interest, description of variable rate basis	-
Interest Rate	5.07%
Mortgage loans payable	23,000	23,142
Orlando, FL [Member] | 6.40% Loan Due in Jul 2017 [Member]
Debt Instrument [Line Items]
Maturity	Jul 2017
Loan bears interest, description of variable rate basis	-
Interest Rate	6.40%
Mortgage loans payable	36,511	36,983
Plantation, FL [Member] | 6.48% Loan Due in Apr 2018 [Member]
Debt Instrument [Line Items]
Maturity	Apr 2018
Loan bears interest, description of variable rate basis	-
Interest Rate	6.48%
Mortgage loans payable	10,585	10,684
Churchill, PA [Member] | 3.50% Loan Due in Aug 2024 [Member]
Debt Instrument [Line Items]
Maturity	Aug 2024
Loan bears interest, description of variable rate basis	-
Interest Rate	3.50%
Mortgage loans payable	4,951	5,049
Oklahoma City, OK [Member]
Debt Instrument [Line Items]
Maturity	Feb 2021
Loan bears interest, description of variable rate basis	-
Mortgage loans payable		$ 9,967