Fair Value of Financial Instruments Measured at Fair Value - Loans, Loan Servicing Rights, Related Notes and Certificates (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	$ 3,230,661	$ 2,798,505
Servicing assets	3,496us-gaap_ServicingAssetAtFairValueAmount	2,181us-gaap_ServicingAssetAtFairValueAmount
Total assets	3,234,157us-gaap_AssetsFairValueDisclosure	2,800,686us-gaap_AssetsFairValueDisclosure
Notes and certificates	3,249,346	2,813,618
Servicing liabilities	4,397	3,973
Total liabilities	3,253,743us-gaap_LiabilitiesFairValueDisclosure	2,817,591us-gaap_LiabilitiesFairValueDisclosure
Level 1 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	0	0
Servicing assets	0	0
Total assets	0	0
Notes and certificates	0	0
Servicing liabilities	0	0
Total liabilities	0	0
Level 2 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	0	0
Servicing assets	0	0
Total assets	0	0
Notes and certificates	0	0
Servicing liabilities	0	0
Total liabilities	0	0
Level 3 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	3,230,661	2,798,505
Servicing assets	3,496	2,181
Total assets	3,234,157	2,800,686
Notes and certificates	3,249,346	2,813,618
Servicing liabilities	4,397	3,973
Total liabilities	$ 3,253,743	$ 2,817,591

Notes and Certificates at fair value

No definition available.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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- Definition

Fair value of financial and nonfinancial obligations.

+ References

+ Details

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- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Glossary Loan

-URI http://asc.fasb.org/extlink&oid=6517073

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- Definition

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 3

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746

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- Definition

Fair value of a liability representing servicing arrangements under which the estimated future revenue from contractually specified servicing fees, late charges, and other ancillary revenues are not expected to adequately compensate the servicer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122492-111745

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 3

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746

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