Indebtedness - Information Regarding Indebtedness (Detail) (USD $) In Thousands, unless otherwise specified					12 Months Ended			12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2012 Mortgage Financing I-V	Dec. 31, 2013 2016 Notes	Dec. 31, 2012 2016 Notes	Dec. 31, 2013 2017 Notes	Dec. 31, 2012 2017 Notes	Dec. 31, 2013 2027 Notes	Dec. 31, 2012 2027 Notes	Dec. 31, 2013 2028 Notes	Dec. 31, 2012 2028 Notes	Dec. 31, 2013 2032 Notes	Dec. 31, 2012 2032 Notes	Dec. 31, 2013 2014 Notes	Dec. 31, 2012 2014 Notes	Dec. 31, 2013 2017 II Notes	Dec. 31, 2012 2017 II Notes	Dec. 31, 2013 Mortgages [Member]	Dec. 31, 2013 Line of Credit
Debt Instrument [Line Items]
Mortgage Loans Payable, Net	$ 580,215		$ 656,329
Unamortized Premiums	(115)		(161)
Mortgage Loans Payable, Gross	580,100		656,168
Senior Unsecured Notes, Net	445,916		474,150			159,566	159,510	54,960	55,385	6,066	6,066	31,883	55,261	10,514	11,500	81,149	79,683	101,778	106,745
Unamortized Discounts	980		2,570
Senior Unsecured Notes, Gross	446,896		476,720
Unsecured Credit Facility	$ 173,000	[1]	$ 98,000	[1]
Interest Rate, Minimum																				4.03%
Interest Rate, Maximum																				8.26%
Interest Rate					4.03%	5.75%		7.50%		7.15%		7.60%		7.75%		6.42%		5.95%
Interest Rate																					1.666%	[1]
Effective Interest Rate, Minimum																				4.03%
Effective Interest Rate, Maximum																				8.26%
Effective Interest Rate						5.91%		7.52%		7.11%		8.13%		7.87%		6.54%		6.37%			1.666%	[1]
Maturity Date Range, Start																				Oct. 01, 2014
Maturity Date Range, End																				Sep. 01, 2022
Maturity Date					Sep. 01, 2022	Jan. 15, 2016		Dec. 01, 2017		May 15, 2027		Jul. 15, 2028		Apr. 15, 2032		Jun. 01, 2014		May 15, 2017			Sep. 29, 2017	[1]

[1] The maturity date may be extended an additional year at our election, subject to certain restrictions.