Fair value Measurements - Fair Values of Financial Assets and Liabilities, Including Derivative Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Apr. 30, 2014	Dec. 31, 2013
Earning assets
Tax indemnification receivable	$ 240,311us-gaap_IncomeTaxReceivable	$ 291,000us-gaap_IncomeTaxReceivable	$ 0us-gaap_IncomeTaxReceivable
Fair Value
Earning assets
Loans held for investment, net	10,228,399		8,541,919
Cash and cash equivalents	2,359,780		2,182,865
Available for sale investments	168,934		102,105
Accrued interest receivable	469,697		356,283
Tax indemnification receivable	240,311		0
Derivative instruments	5,238		6,761
Total	13,472,359		11,189,933
Interest-bearing liabilities
Accrued interest payable	16,082		13,097
Derivative instruments	28,688		6,149
Total interest-bearing liabilities	10,590,151		9,033,241
Fair Value \| Money market, savings and NOW accounts
Interest-bearing liabilities
Deposits	5,231,736		4,029,881
Fair Value \| Certificates of Deposit
Interest-bearing liabilities
Deposits	5,313,645		4,984,114
Carrying Value
Earning assets
Loans held for investment, net	9,509,786		7,931,377
Cash and cash equivalents	2,359,780		2,182,865
Available for sale investments	168,934		102,105
Accrued interest receivable	469,697		356,283
Tax indemnification receivable	240,311		0
Derivative instruments	5,238		6,761
Total	12,753,746		10,579,391
Interest-bearing liabilities
Accrued interest payable	16,082		13,097
Derivative instruments	28,688		6,149
Total interest-bearing liabilities	10,585,324		9,020,796
Carrying Value \| Money market, savings and NOW accounts
Interest-bearing liabilities
Deposits	5,231,736		4,029,881
Carrying Value \| Certificates of Deposit
Interest-bearing liabilities
Deposits	5,308,818		4,971,669
Difference
Earning assets
Loans held for investment, net	718,613		610,542
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	718,613		610,542
Interest-bearing liabilities
Accrued interest payable	0		0
Derivative instruments	0		0
Total interest-bearing liabilities	(4,827)		(12,445)
Excess of net asset fair value over carrying value	713,786		598,097
Difference \| Money market, savings and NOW accounts
Interest-bearing liabilities
Deposits	0		0
Difference \| Certificates of Deposit
Interest-bearing liabilities
Deposits	$ (4,827)		$ (12,445)

Accrued Interest Receivable, Fair Value Disclosure

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Excess of net asset fair value over carrying value.

+ References

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Fair value portion of accrued expenses.

+ References

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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-Paragraph 20

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

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-Publisher FASB

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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.

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-Glossary Cash Equivalents

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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

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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.

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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.

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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.

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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

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

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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

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-Publisher FASB

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