Debt - Mortgage Loans Payable (Parenthetical) (Detail) - Mortgage Loans Payable [Member]					12 Months Ended
	Aug. 19, 2016	May 19, 2016	May 12, 2016	Apr. 28, 2016	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
LIBOR rate					0.77167%	0.4295%
Chicago, IL [Member]
Debt Instrument [Line Items]
Date of loan repayment				Apr. 28, 2016
Greensboro, North Carolina Sale [Member]
Debt Instrument [Line Items]
Date of loan repayment			May 12, 2016
Lisle IL [Member]
Debt Instrument [Line Items]
Date of loan repayment	Aug. 19, 2016
Houston, TX and Stamford, CT [Member]
Debt Instrument [Line Items]
Date of loan repayment		May 19, 2016
Percentage of proceeds from sale of property used to repay mortgage					100.00%
3.22% Loan Due in Jun 2018 [member]
Debt Instrument [Line Items]
Mortgage loan, LIBOR rate					1.50%