Debt - Mortgage Loans Payable (Parenthetical) (Detail)	6 Months Ended
	Jun. 30, 2013
Debt Instrument [Line Items]
LIBOR Rate	0.19465%
Three Percent Loan Due August Two Thousand And Fourteen [Member]
Debt Instrument [Line Items]
Debt instrument basis spread on floor rate	0.50%
Debt instrument interest rate cap basis spread at LIBOR	0.50%
Zero Percent Loan Due October Two Thousand And Fourteen [Member]
Debt Instrument [Line Items]
Debt instrument interest rate cap basis spread at LIBOR	1.00%
Three Point Five Percent Due May Two Thousand Sixteen [Member]
Debt Instrument [Line Items]
Debt instrument basis spread on floor rate	1.00%
Debt instrument interest rate cap basis spread at LIBOR	1.75%
Amherst, NY [Member] | Five Point Six Five Percent Loan Due October Two Thousand And Thirteen [Member]
Debt Instrument [Line Items]
Maturity date of loan	Jul. 26, 2013
Philadelphia Pa [Member] | Two Point Five Percent Due May Two Thousand Sixteen [Member]
Debt Instrument [Line Items]
Mortgage loan, LIBOR rate	0.50%