Derivatives - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended			9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Series F Preferred Stock [Member]	Oct. 31, 2008 Series F Preferred Stock [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						5.935%
Notional value of interest rate swap agreement							$ 50,000
Treasury rate of agreement							5.2175%
Mark-to-Market (Loss) Gain on Interest Rate Protection Agreements	0	(29)	52	(334)
Settlement payments of mark-to-market gains or losses	214	326	774	865
Amortization to be reclassified from OCI into income			1,846
Number of years of long dated treasuries			30 years
Outstanding settlement payment due on the agreement	$ 214		$ 214		$ 305