Derivatives - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended			6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013 Series F Preferred Units [Member]	Oct. 31, 2008 Series F Preferred Units [Member]
Derivative [Line Items]
Minimum fixed coupon rate of preferred stock						2.375%
Number of years of U.S. treasury rate one						30 years
Number of years of U.S. treasury rate two						10 years
LIBOR rate						3 month LIBOR
New coupon rate of preferred stock						5.515%
Notional value of interest rate swap agreement							$ 50,000
Treasury rate of agreement							5.2175%
Mark-to-Market Gain (Loss) on Interest Rate Protection Agreements	56	(429)	52	(305)
Settlement payments of mark-to-market gains or losses	267	247	560	539
Amortization to be reclassified from OCI into income			2,326
Number of years of long dated treasuries			30 years
Outstanding settlement payment due on the agreement	$ 267		$ 267		$ 305