Fair Value Measurements - Trust Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets
Assets measured at fair value on a recurring basis	$ 10,725	$ 19,713
Securities Carried at Fair Value [Member]
Assets
Assets measured at fair value on a recurring basis	10,360	19,694
Loan Securities Carried at Fair Value [Member]
Assets
Assets measured at fair value on a recurring basis	226	11
Interest Rate Contract [Member]
Assets
Assets measured at fair value on a recurring basis	139
Interest Rate Caps [Member]
Assets
Assets measured at fair value on a recurring basis		8
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Assets measured at fair value on a recurring basis	10,360	19,694
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Securities Carried at Fair Value [Member]
Assets
Assets measured at fair value on a recurring basis	10,360	19,694
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Loan Securities Carried at Fair Value [Member]
Assets
Assets measured at fair value on a recurring basis
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Interest Rate Contract [Member]
Assets
Assets measured at fair value on a recurring basis
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Interest Rate Caps [Member]
Assets
Assets measured at fair value on a recurring basis
Significant Other Observable Inputs (Level 2) [Member]
Assets
Assets measured at fair value on a recurring basis	139	8
Significant Other Observable Inputs (Level 2) [Member] | Securities Carried at Fair Value [Member]
Assets
Assets measured at fair value on a recurring basis
Significant Other Observable Inputs (Level 2) [Member] | Loan Securities Carried at Fair Value [Member]
Assets
Assets measured at fair value on a recurring basis
Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Contract [Member]
Assets
Assets measured at fair value on a recurring basis	139
Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Caps [Member]
Assets
Assets measured at fair value on a recurring basis		8
Significant Unobservable Inputs (Level 3) [Member]
Assets
Assets measured at fair value on a recurring basis	226	11
Significant Unobservable Inputs (Level 3) [Member] | Securities Carried at Fair Value [Member]
Assets
Assets measured at fair value on a recurring basis
Significant Unobservable Inputs (Level 3) [Member] | Loan Securities Carried at Fair Value [Member]
Assets
Assets measured at fair value on a recurring basis	226	11
Significant Unobservable Inputs (Level 3) [Member] | Interest Rate Contract [Member]
Assets
Assets measured at fair value on a recurring basis
Significant Unobservable Inputs (Level 3) [Member] | Interest Rate Caps [Member]
Assets
Assets measured at fair value on a recurring basis