Summary of Held-to-Maturity and Available-for-Sale Securities Having Continuous Unrealized Loss Position (Parenthetical) (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	$ 2,603,000	$ 7,073,000
Equity Securities
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	630,000	2,900,000
Equity Securities | US Large Cap Equity Securities
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss		2,200,000
Principal balance of fund		30,200,000
Equity Securities | Financial Institution
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss		709,000
Principal balance of fund	$ 1,700,000	$ 1,700,000