Fair value Measurements - Fair Values of Financial Assets and Liabilities, Including Derivative Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Earning assets
Tax indemnification receivable	$ 227,157us-gaap_IncomeTaxReceivable	$ 240,311us-gaap_IncomeTaxReceivable
Estimate of Fair Value Measurement [Member]
Earning assets
Loans held for investment, net	11,878,508	10,228,399
Cash and cash equivalents	875,622	2,359,780
Available-for-sale investments	170,831	168,934
Accrued interest receivable	541,355	469,697
Tax indemnification receivable	227,157	240,311
Derivative instruments	25,410	5,238
Total earning assets	13,718,883	13,472,359
Interest-bearing liabilities
Accrued interest payable	22,624	16,082
Derivative instruments	38,063	28,688
Total interest-bearing liabilities	10,544,488	10,590,151
Estimate of Fair Value Measurement [Member] \| Money market, savings and NOW accounts
Interest-bearing liabilities
Deposits	5,209,320	5,231,736
Estimate of Fair Value Measurement [Member] \| Certificates of Deposit
Interest-bearing liabilities
Deposits	5,274,481	5,313,645
Carrying Value
Earning assets
Loans held for investment, net	10,909,014	9,509,786
Cash and cash equivalents	875,622	2,359,780
Available-for-sale investments	170,831	168,934
Accrued interest receivable	541,355	469,697
Tax indemnification receivable	227,157	240,311
Derivative instruments	25,410	5,238
Total earning assets	12,749,389	12,753,746
Interest-bearing liabilities
Accrued interest payable	22,624	16,082
Derivative instruments	38,063	28,688
Total interest-bearing liabilities	10,528,440	10,585,324
Carrying Value \| Money market, savings and NOW accounts
Interest-bearing liabilities
Deposits	5,209,320	5,231,736
Carrying Value \| Certificates of Deposit
Interest-bearing liabilities
Deposits	5,258,433	5,308,818
Changes Measurement [Member]
Earning assets
Loans held for investment, net	969,494	718,613
Cash and cash equivalents	0	0
Available-for-sale investments	0	0
Accrued interest receivable	0	0
Tax indemnification receivable	0	0
Derivative instruments	0	0
Total earning assets	969,494	718,613
Interest-bearing liabilities
Accrued interest payable	0	0
Derivative instruments	0	0
Total interest-bearing liabilities	(16,048)	(4,827)
Excess of net asset fair value over carrying value	953,446	713,786
Changes Measurement [Member] \| Money market, savings and NOW accounts
Interest-bearing liabilities
Deposits	0	0
Changes Measurement [Member] \| Certificates of Deposit
Interest-bearing liabilities
Deposits	$ (16,048)	$ (4,827)

Accrued Interest Receivable, Fair Value Disclosure

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- Definition

Excess of net asset fair value over carrying value.

+ References

No definition available.

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- Definition

Fair value portion of accrued expenses.

+ References

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 FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.20)

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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)

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

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- Definition

Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

+ References

No definition available.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

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-Paragraph 5

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-Topic 825

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-Name Accounting Standards Codification

-Topic 210

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-Topic 210

-SubTopic 20

-Section 55

-Paragraph 10

-URI http://asc.fasb.org/extlink&oid=36459792&loc=SL20226008-175313

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- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

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- Definition

Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities.

+ References

No definition available.

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- Definition

Carrying amount as of the balance sheet date of income taxes previously overpaid to tax authorities (such as U.S. Federal, state and local tax authorities) representing refunds of overpayments or recoveries based on agreed-upon resolutions of disputes. Also called income tax refund receivable.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.8)

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 8

-Article 5

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 5

-Subparagraph c

-Article 7

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- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Available-for-Sale Securities

-URI http://asc.fasb.org/extlink&oid=6505594

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-URI http://asc.fasb.org/extlink&oid=6526789

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-Section 25

-Paragraph 1

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-Section 03

-Paragraph 1

-Subparagraph a, f, g

-Article 7

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-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 35

-Paragraph 1

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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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