Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Schedule of Reconciliation of Residual Assets (Detail)

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Fair Value Measurements - Schedule of Reconciliation of Residual Assets (Detail) (USD $)
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]        
Balance, beginning of period $ 4,436,199 $ 4,647,044 $ 4,638,579 $ 4,870,715
Accretion 118,983 76,418 246,258 225,074
Additions 9,975 28,837 9,975 28,837
Collections (249,413) (275,314) (370,818) (500,155)
Unrealized gain (loss) on residual assets 126,569 190,321 (81,681) 42,835
Balance, end of period $ 4,442,313 $ 4,667,306 $ 4,442,313 $ 4,667,306