Debt - Mortgage Loans Payable (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Interest rate, description	LIBOR plus 3%
Mortgage loans payable	$ 308,049	$ 280,576
Three Percent Loan Due August Two Thousand and Fourteen [Member] | Memphis, TN [Member]
Debt Instrument [Line Items]
Maturity	Aug 2014
Interest rate, description	Libor + 2.5%
Interest rate	3.00%
Mortgage loans payable	13,197	13,408
Two Point Six Nine Percent Loan Due October Two Thousand and Fourteen [Member] | Lisle, IL [Member]
Debt Instrument [Line Items]
Maturity	Oct 2014
Interest rate, description	Libor + 2.5%
Interest rate	2.69%
Mortgage loans payable	5,752	5,752
Six Point Two Five Percent Loan Due April Two Thousand and Fifteen [Member] | Chicago, IL [Member]
Debt Instrument [Line Items]
Maturity	Apr 2015
Interest rate, description
Interest rate	6.25%
Mortgage loans payable	8,619	8,700
Five Point Seven Five Percent Loan Due March Two Thousand and Sixteen [Member] | Chicago, IL [Member]
Debt Instrument [Line Items]
Maturity	Mar 2016
Interest rate, description
Interest rate	5.75%
Mortgage loans payable	19,941	20,200
Six Point Zero Nine Percent Loan Due April Two Thousand and Sixteen [Member] | Houston, TX [Member]
Debt Instrument [Line Items]
Maturity	Apr 2016
Interest rate, description
Interest rate	6.05%
Mortgage loans payable	48,460	52,052
Three Point Five Percent Due May Two Thousand Sixteen [Member] | New York, NY [Member]
Debt Instrument [Line Items]
Maturity	May 2016
Interest rate, description	Libor + 2.5%
Interest rate	3.50%
Mortgage loans payable	51,982	51,982
Two Point Five Percent Due May Two Thousand Sixteen [Member] | Philadelphia Pa [Member]
Debt Instrument [Line Items]
Maturity	May 2016
Interest rate, description	Libor + 2.0%
Interest rate	2.50%
Mortgage loans payable	42,684
Six Point Two Two Percent Loan Due August Two Thousand and Sixteen [Member] | Greensboro, NC [Member]
Debt Instrument [Line Items]
Maturity	Aug 2016
Interest rate, description
Interest rate	6.22%
Mortgage loans payable	14,837	15,139
Five Point Five Five Percent Loans Due March Two Thousand Seventeen [Member] | Lisle, IL [Member]
Debt Instrument [Line Items]
Maturity	Mar 2017
Interest rate, description
Interest rate	5.55%
Mortgage loans payable	5,488	5,543
Five Point Zero Seven Percent Loan Due January Two Thousand and Seventeen [Member] | Cerritos, CA [Member]
Debt Instrument [Line Items]
Maturity	Jan 2017
Interest rate, description
Interest rate	5.07%
Mortgage loans payable	23,153	23,184
Six Point Four Zero Percent Loans Due July Two Thousand Seventeen [Member] | Orlando, FL [Member]
Debt Instrument [Line Items]
Maturity	Jul 2017
Interest rate, description
Interest rate	6.40%
Mortgage loans payable	37,138	37,580
Six Point Four Five Percent Loans Due April Two Thousand Eighteen [Member] | Plantation, FL [Member]
Debt Instrument [Line Items]
Maturity	Apr 2018
Interest rate, description
Interest rate	6.45%
Mortgage loans payable	10,717	10,811
Three Point Nine Five Percent Loan Due October Two Thousand and Twenty Two [Member] | Meriden CT [Member]
Debt Instrument [Line Items]
Maturity	Oct 2022
Interest rate, description
Interest rate	3.95%
Mortgage loans payable	21,000	21,000
Three Point Five Percent Due August Two Thousand and Twenty Four [Member] | Churchill [Member]
Debt Instrument [Line Items]
Maturity	Aug 2024
Interest rate, description
Interest rate	3.50%
Mortgage loans payable	5,081
Five Point Six Five Percent Loan Due October Two Thousand and Thirteen [Member] | Amherst, NY [Member]
Debt Instrument [Line Items]
Maturity	Oct 2013
Interest rate, description
Interest rate	5.65%
Mortgage loans payable		$ 15,225