SECURITIES - Additional Information (Detail) (USD $)							6 Months Ended				6 Months Ended
	Jun. 30, 2012 Investment	Dec. 31, 2011	Jun. 30, 2011	Jun. 30, 2012 Private issue collateralized mortgage obligations	Dec. 31, 2011 Private issue collateralized mortgage obligations	Jun. 30, 2012 Private issue collateralized mortgage obligations Noninvestment grade	Jun. 30, 2012 Agency Securities Investment	Jun. 30, 2012 Collateralized Mortgage Backed Securities Investment	Dec. 31, 2011 Collateralized Mortgage Backed Securities	Jun. 30, 2012 Federal Home Loan Mortgage Corporation	Jun. 30, 2012 Auction Rate Securities Investment	Jun. 30, 2012 Pass-through certificates collateralized by the Freddie Mac preferred stock
Schedule of Investments [Line Items]
Unrealized gains on securities available-for-sale included in accumulated other comprehensive income, net of deferred taxes	$ 12,082,000	$ 11,128,000
Unrealized gains on securities available-for-sale included in accumulated other comprehensive income, deferred taxes	6,500,000	6,000,000
Investment securities with unrealized losses that are considered temporary	29,533,000	62,873,000		10,094,000	10,641,000	9,300,000		19,439,000	38,091,000
Number of investment securities which had unrealized losses for twelve months or longer	18
Investment securities with unrealized losses for twelve months or longer	10,132,000	14,853,000		10,094,000	10,641,000			38,000	66,000
Number of available for sale securities sold							1	6			1
Number of preferred shares sold										587,481
Other than temporary impairment losses												14,950,000
Tender offer issued by DNP to buy back auction rate security pools											96.00%
Security pledged as collateral, amortized cost	431,100,000		515,800,000
Security pledged as collateral, fair value	$ 448,800,000		$ 532,200,000