Equity and Noncontrolling Interests - Additional Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	1 Months Ended	6 Months Ended		3 Months Ended	6 Months Ended			3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended
	Dec. 31, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2012 At-The-Market Common Equity Sales Program [Member]	Jun. 30, 2012 At-The-Market Common Equity Sales Program [Member]	Jun. 30, 2013 At-The-Market Common Equity Sales Program [Member]	May 31, 2012 At-The-Market Common Equity Sales Program [Member]	Jun. 30, 2012 At-The-Market Common Equity Sales Program [Member] Gross [Member]	Jun. 30, 2012 At-The-Market Common Equity Sales Program [Member] Gross [Member]	Jun. 30, 2012 At-The-Market Common Equity Sales Program [Member] Net [Member]	Jun. 30, 2012 At-The-Market Common Equity Sales Program [Member] Net [Member]
Equity And Noncontrolling Interests [Line Items]
Common stock, shares authorized	100,000	100,000					4,000
Common stock, shares issued						4,000
Sale of common stock, shares				97	414
Proceeds from sales of common stock			$ 18,625					$ 4,847	$ 19,159	$ 4,643	$ 18,625
Sales price per share				$ 50.23	$ 46.33
Stock repurchase program, authorized amount	200,000
Shares of common stock repurchased		0	0
Redeemable common units	7,159	7,093
Noncontrolling interests in the Operating Partnership, net book value	$ 2,820	$ 2,889