Debt - Mortgage Loans Payable (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Loan bears interest, description of variable rate basis	LIBOR plus 3%
Mortgage loans payable	$ 444,933,000	$ 280,576,000
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	13,125,000	13,408,000
Lisle, IL [Member] | 2.67% 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	2.67%
Mortgage loans payable	5,752,000	5,752,000
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	5,470,000	5,543,000
Chicago, IL [Member] | 5.50% Loan Due in Apr 2015 [Member]
Debt Instrument [Line Items]
Maturity	Apr 2015
Loan bears interest, description of variable rate basis
Interest rate	5.50%
Mortgage loans payable	8,579,000	8,700,000
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	19,856,000	20,200,000
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	6.01%
Mortgage loans payable	47,201,000	52,052,000
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	64,635,000
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	51,950,000	51,982,000
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	42,440,000
Greensboro, NC [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	14,735,000	15,139,000
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	24,390,000
San Pedro [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	12,195,000
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	48,780,000
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	23,142,000	23,184,000
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	36,983,000	37,580,000
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	10,684,000	10,811,000
Oklahoma City [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	9,967,000
Meriden CT [Member] | 3.95% Loan Due in Oct 2022 [Member]
Debt Instrument [Line Items]
Maturity	Oct 2022
Loan bears interest, description of variable rate basis
Interest rate	3.95%
Mortgage loans payable		21,000,000
Churchill [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	5,049,000
Amherst, NY [Member]
Debt Instrument [Line Items]
Maturity	N/A
Loan bears interest, description of variable rate basis
Mortgage loans payable		$ 15,225,000