Subsequent Events - Additional Information (Detail) (USD $)				6 Months Ended
	Jun. 30, 2011	Jun. 08, 2011	May 31, 2011	Jun. 30, 2011 Common Stock Subsequent Event 1	Jun. 30, 2011 Subsequent Event 1 Entity	Jun. 30, 2011 Subsequent Event 1 Series B Preferred Stock	Jun. 30, 2011 Common Stock Subsequent Event 2	Jun. 30, 2011 Subsequent Event 2 Entity	Jun. 30, 2011 Maximum Term Loan	Jun. 30, 2011 Minimum Term Loan	Jun. 30, 2011 Term Loan
Subsequent Event [Line Items]
Number of closed acquisition					35			16
Acquisition date					Jul. 01, 2011			Aug. 01, 2011
Purchase price			$ 1,430,000,000		$ 452,000,000			$ 436,000,000
Stock issued for the Acquisition Properties, share				282,759		286,207	1,379,310
Stock issued for the Acquisition Properties, aggregate stated value				16,400,000		16,600,000	80,000,000
Mortgage debt assumed for the Acquisition Properties, aggregate stated value								226,000,000
cash paid for the Acquisition Properties					419,000,000			130,000,000
Acquisition escrow deposit	300,000,000	275,000,000	25,000,000
Debt, maturity date											Jun. 30, 2017
Start date to repay debt without penalty on prepayment											Jul. 01, 2014
Debt, percentage of prepayment penalty											2.00%
Debt, arrangement fee											500,000
Debt, upfront fee											1,300,000
Debt, annual adiministrative agency fee											$ 20,000
Swap, fixed interest rate											1.11%
Spread over LIBOR											2.15%
Initial estimated all-in interest rate											3.26%
Debt instrument, interest rate based on a margin over LIBOR									2.80%	1.85%