Variable Interest Entities - Principal Provisions of Debt (Detail) (USD $)	Jun. 30, 2013 Y	Dec. 31, 2012 Y
Debt Instrument [Line Items]
Principal Outstanding	$ 11,308,642	$ 12,484,729
Weighted Average Interest Rate
Weighted Average Remaining Maturity in Years
Senior Secured Notes [Member]
Debt Instrument [Line Items]
Principal Outstanding	10,379,364	11,409,825
Weighted Average Interest Rate	1.04%	1.30%
Weighted Average Remaining Maturity in Years	7.0	7.3
Subordinated Notes [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 929,278	$ 1,074,904
Weighted Average Interest Rate
Weighted Average Remaining Maturity in Years	7.6	7.7

Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 20

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 9

Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant