Investment Securities - Summary of Continuous Loss Position of Securities (Detail) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Investment [Line Items]
Fair Value, Less than 12 months	$ 428,778,000	$ 194,146,000
Gross Unrealized Holding Losses, Less than 12 months	5,840,000	1,109,000
Fair Value, 12 months or longer	7,667,000	70,017,000
Gross unrealized holding losses, 12 months or longer	88,000	859,000
Fair Value	436,445,000	264,163,000
Gross Unrealized Holding Losses	5,928,000	1,968,000
Gross Unrealized Holding Losses	0
CMO [Member]
Investment [Line Items]
Fair Value, Less than 12 months
Gross Unrealized Holding Losses, Less than 12 months
Fair Value, 12 months or longer
Gross unrealized holding losses, 12 months or longer
Fair Value
Gross Unrealized Holding Losses
Government agency [Member]
Investment [Line Items]
Fair Value, Less than 12 months	182,843,000	51,134,000
Gross Unrealized Holding Losses, Less than 12 months	1,543,000	248,000
Fair Value	182,843,000	51,134,000
Gross Unrealized Holding Losses	1,543,000	248,000
Residential Mortgage-Backed Securities [Member]
Investment [Line Items]
Fair Value, Less than 12 months	173,748,000	55,118,000
Gross Unrealized Holding Losses, Less than 12 months	3,415,000	127,000
Fair Value	173,748,000	55,118,000
Gross Unrealized Holding Losses	3,415,000	127,000
CMO's / REMIC's - residential [Member]
Investment [Line Items]
Fair Value, Less than 12 months	45,399,000	74,784,000
Gross Unrealized Holding Losses, Less than 12 months	539,000	572,000
Fair Value, 12 months or longer	5,460,000	69,042,000
Gross unrealized holding losses, 12 months or longer	17,000	838,000
Fair Value	50,859,000	143,826,000
Gross Unrealized Holding Losses	556,000	1,410,000
Municipal bonds [Member]
Investment [Line Items]
Fair Value, Less than 12 months	26,788,000	13,110,000
Gross Unrealized Holding Losses, Less than 12 months	343,000	162,000
Fair Value, 12 months or longer	2,207,000	975,000
Gross unrealized holding losses, 12 months or longer	71,000	21,000
Fair Value	28,995,000	14,085,000
Gross Unrealized Holding Losses	414,000	183,000
Other Securities [Member]
Investment [Line Items]
Fair Value, Less than 12 months
Gross Unrealized Holding Losses, Less than 12 months
Fair Value, 12 months or longer
Gross unrealized holding losses, 12 months or longer
Fair Value
Gross Unrealized Holding Losses

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Amount of the excess of amortized cost basis over fair value of securities that have been in a loss position for twelve months or longer for securities which are categorized neither as held-to-maturity nor trading securities.

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This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

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