Securities - Held to Maturity with Unrealized Losses (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, Losses less than 12 months, Fair Value	$ 4,202	$ 87,852
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	36	259
Held to maturity securities, Losses 12 months or longer, Fair value	41,997	54,445
Held to maturity securities, Losses 12 months or longer, Gross Unrealized Losses	430	682
Held to maturity securities, Total, Fair value	46,199	142,297
Held to maturity securities, Total, Gross Unrealized Losses	466	941
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, Losses less than 12 months, Fair Value	1,667
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	30
Held to maturity securities, Total, Fair value	1,667
Held to maturity securities, Total, Gross Unrealized Losses	30
Mortgage-backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, Losses less than 12 months, Fair Value	2,535
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	0
Held to maturity securities, Total, Fair value	2,535
Held to maturity securities, Total, Gross Unrealized Losses	0
Collateralized mortgage obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, Losses less than 12 months, Fair Value		87,852
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	6	259
Held to maturity securities, Losses 12 months or longer, Fair value	41,997	54,445
Held to maturity securities, Losses 12 months or longer, Gross Unrealized Losses	430	682
Held to maturity securities, Total, Fair value	41,997	142,297
Held to maturity securities, Total, Gross Unrealized Losses	$ 436	$ 941