Debt - Mortgage Loans Payable (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Loan bears interest, description of variable rate basis	LIBOR plus 3%
Mortgage loans payable	$ 296,954	$ 444,933
Lisle, IL [Member] | Two Point Six Seven Percent Loan Due October Two Thousand And Fifteen [Member]
Debt Instrument [Line Items]
Maturity	Oct 2015
Loan bears interest, description of variable rate basis	Libor + 2.5 %
Interest Rate	2.67%
Mortgage loans payable	5,713	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	5,392	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	19,491	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	51,034	51,950
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	22,462	24,390
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	44,923	48,780
Houston, TX [Member]
Debt Instrument [Line Items]
Maturity	N/A
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	59,524	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	36,347	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	10,550	10,684
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	4,918	5,049
Oklahoma City [Member]
Debt Instrument [Line Items]
Maturity	N/A
Loan bears interest, description of variable rate basis	-
Mortgage loans payable		9,967
Memphis, TN [Member]
Debt Instrument [Line Items]
Maturity	N/A
Loan bears interest, description of variable rate basis	-
Mortgage loans payable		13,125
San Pedro [Member]
Debt Instrument [Line Items]
Maturity	N/A
Loan bears interest, description of variable rate basis	-
Mortgage loans payable		12,195
Philadelphia, PA [Member]
Debt Instrument [Line Items]
Maturity	N/A
Loan bears interest, description of variable rate basis	-
Mortgage loans payable		$ 42,440