Debt - Mortgage Loans Payable (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Loan bears interest, description of variable rate basis	LIBOR plus 3%
Mortgage loans payable	$ 474,107	$ 444,933
Memphis, TN [Member] | 3.00% Loan Due in Aug 2014 [Member]
Debt Instrument [Line Items]
Maturity	Aug 2014
Loan bears interest, description of variable rate basis	Libor + 2.5%
Interest Rate	3.00%
Mortgage loans payable	12,980	13,125
Lisle, IL [Member] | 2.69% Loan Due in Oct 2014 [Member]
Debt Instrument [Line Items]
Maturity	Oct 2014
Loan bears interest, description of variable rate basis	Libor + 2.5%
Interest Rate	2.69%
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	5,430	5,470
Norridge, IL [Member] | 6% Loan Due in Apr 2015 [Member]
Debt Instrument [Line Items]
Maturity	Aug 2015
Loan bears interest, description of variable rate basis	Libor + 5.75%
Interest Rate	6.00%
Mortgage loans payable	42,500	0
Chicago, IL [Member]
Debt Instrument [Line Items]
Maturity	n/a
Loan bears interest, description of variable rate basis	-
Mortgage loans payable	0	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	19,671	19,856
Houston, TX [Member] | 6.01% Loan Due in Apr 2016 [Member]
Debt Instrument [Line Items]
Maturity	Apr 2016
Loan bears interest, description of variable rate basis	-
Interest Rate	5.93%
Mortgage loans payable	44,589	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
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	51,465	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	41,950	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	14,529	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
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	23,121	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	36,667	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	10,617	10,684
Oklahoma City, OK [Member] | 5.70 % Loan Due in Feb 2021 [Member]
Debt Instrument [Line Items]
Maturity	Feb 2021
Loan bears interest, description of variable rate basis	-
Interest Rate	5.70%
Mortgage loans payable	9,852	9,967
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	$ 4,984	$ 5,049