Indebtedness - Schedule of Indebtedness (Detail) (USD $) In Thousands, unless otherwise specified			12 Months Ended		12 Months Ended		9 Months Ended	12 Months Ended			12 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Senior Notes [Member]	Dec. 31, 2011 Senior Notes [Member]	Dec. 31, 2012 Senior Notes [Member] Minimum [Member]	Dec. 31, 2012 Senior Notes [Member] Maximum [Member]	Sep. 30, 2012 Unsecured Bank Term Loan [Member]	Dec. 31, 2012 Unsecured Bank Term Loan [Member]	Dec. 31, 2012 Lines of Credit [Member]	Dec. 31, 2011 Lines of Credit [Member]	Dec. 31, 2012 Secured Mortgage Notes [Member]	Dec. 31, 2011 Secured Mortgage Notes [Member]	Dec. 31, 2012 Secured Mortgage Notes [Member] Minimum [Member]	Dec. 31, 2012 Secured Mortgage Notes [Member] Maximum [Member]
Debt Instrument [Line Items]
Payment Terms			Int.					Int.	Int.		Prin. and Int.
Interest Rate, minimum			3.375%								4.88%
Interest Rate, maximum			4.75%								5.99%
Interest Rate, spread over LIBOR							1.90%	1.70%	1.225%
Debt instrument, Maturity Date					2017	2022		2018	2016				2015	2019
Unsecured debt			$ 400,000	$ 375,775				$ 300,000		$ 135,000
Secured debt											402,464	459,668
Total	$ 1,102,464	$ 970,443