Derivatives - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Derivative Financial Instruments, Liabilities [Member]	Oct. 31, 2008 Derivative Financial Instruments, Liabilities [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				5.285%
Notional value of interest rate swap agreement					$ 50,000
Treasury rate				5.2175%
Settlement payments of Mark-to- Market gains or losses	1,169	574
Mark-to-Market Loss on Interest Rate Protection Agreement	328	1,718	1,107
Amortization to be reclassified from OCI into Income	$ 2,421
Number of years of long dated treasuries	30 years