Investment Securities - Investments' Gross Unrealized Losses and Fair Value Aggregated by Investment Category and Length of Time in Continuous Unrealized Loss Position (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	$ 16,844	$ 6,176
Less than 12 Months Gross Unrealized Losses	80	16
12 Months or Longer Fair Value	194	163
12 Months or Longer Gross Unrealized Losses	5,881	5,572
Total Fair Value	17,038	6,339
Total Gross Unrealized Losses	5,961	5,588
State and municipal
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	4,524
Less than 12 Months Gross Unrealized Losses	19
12 Months or Longer Fair Value
12 Months or Longer Gross Unrealized Losses
Total Fair Value	4,524
Total Gross Unrealized Losses	19
U.S. Government-sponsored mortgage-backed securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	12,320	6,176
Less than 12 Months Gross Unrealized Losses	61	16
12 Months or Longer Fair Value
12 Months or Longer Gross Unrealized Losses
Total Fair Value	12,320	6,176
Total Gross Unrealized Losses	61	16
Corporate Bonds and Notes
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value
Less than 12 Months Gross Unrealized Losses
12 Months or Longer Fair Value	194	163
12 Months or Longer Gross Unrealized Losses	5,881	5,572
Total Fair Value	194	163
Total Gross Unrealized Losses	$ 5,881	$ 5,572