Gross Unrealized Losses and Fair Value by Length of Time for Held-To-Maturity Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012 OptionPlan	Dec. 31, 2011 OptionPlan
Held-to-Maturity Securities
Gain (Loss) on Investments [Line Items]
Number of securities	14	1
Fair Value	$ 26,829	$ 541
Less than 12 months	152	1
More than 12 months	0	0
Total Unrealized Losses	152	1
State and municipal
Gain (Loss) on Investments [Line Items]
Number of securities	13	1
Fair Value	16,868	541
Less than 12 months	123	1
More than 12 months	0	0
Total Unrealized Losses	123	1
State and municipal | Held-to-Maturity Securities
Gain (Loss) on Investments [Line Items]
Number of securities	1
Fair Value	9,961
Less than 12 months	29
More than 12 months	0
Total Unrealized Losses	$ 29