Derivatives - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 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				5.325%
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	(4)	124
Settlement payments of mark-to-market gains or losses	293	292
Amortization to be reclassified from OCI into Income	2,457
Number of years of long dated treasuries	30 years
Outstanding settlement payment due	$ 293		$ 305