Debt - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013
Debt Disclosure [Abstract]
Senior notes principal amount	$ 600,000
Senior notes effective interest rate	3.97%
Senior notes maturity	Sep. 15, 2022
Senior notes interest rate	3.95%
Commencement date of senior notes payment	Mar. 15, 2013
Frequency of senior notes payment	Semi-annually in arrears on March 15 and September 15
Repurchase agreement maximum loan borrowing capacity	25,000
Repurchase agreement outstanding amount	0
Repurchase agreement borrowing base limitations	$ 0
Expiration date of repurchase agreement	Jul. 31, 2013

Expiration date of repurchase agreement.

No definition available.

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- Definition

Borrowing base limitations that reduce the amount available for borrowings under the repurchase agreement.

+ References

No definition available.

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- Definition

Borrowing capacity under the repurchase agreement.

+ References

No definition available.

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- Details

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- Definition

Date the debt agreement requires the first payment to be made, in CCYY-MM-DD format.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

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- Definition

The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

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-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16, 20

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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- Definition

Description of the frequency of periodic payments (monthly, quarterly, annual).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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- Definition

Interest rate stated in the contractual debt agreement.

+ References

+ Details

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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- Definition

Carrying value as of the balance sheet date of the outstanding short-term borrowings under a revolving line of credit used by mortgage bankers to finance the origination or purchase of loans.

+ References

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