Fair Value Measurements - Trust Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Assets and Liabilities
Assets measured at fair value on a recurring basis	$ 7,286	$ 19,713
Securities Carried at Fair Value [Member]
Assets and Liabilities
Assets measured at fair value on a recurring basis	7,074	19,694
Loan Securities Carried at Fair Value [Member]
Assets and Liabilities
Assets measured at fair value on a recurring basis	226	11
Interest Rate Hedges [Member]
Assets and Liabilities
Assets measured at fair value on a recurring basis	(14)	8
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets and Liabilities
Assets measured at fair value on a recurring basis	7,074	19,694
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Securities Carried at Fair Value [Member]
Assets and Liabilities
Assets measured at fair value on a recurring basis	7,074	19,694
Significant Other Observable Inputs (Level 2) [Member]
Assets and Liabilities
Assets measured at fair value on a recurring basis	(14)	8
Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Hedges [Member]
Assets and Liabilities
Assets measured at fair value on a recurring basis	(14)	8
Significant Unobservable Inputs (Level 3) [Member]
Assets and Liabilities
Assets measured at fair value on a recurring basis	226	11
Significant Unobservable Inputs (Level 3) [Member] | Loan Securities Carried at Fair Value [Member]
Assets and Liabilities
Assets measured at fair value on a recurring basis	$ 226	$ 11