Shareholders' Equity - Issued and Outstanding Preferred Stock (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Carrying value	$ 1,231,500us-gaap_PreferredStockValue	$ 1,231,500us-gaap_PreferredStockValue
Series D Fixed Rate Non-cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	50,000	50,000
Preferred stock, shares outstanding	500,000	50,000
Carrying value	500,000	50,000
Series E Fixed-to-Floating Rate Non-cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	350,000	350,000
Preferred stock, shares outstanding	350,000	350,000
Carrying value	350,000	350,000
Series A Fixed Rate Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	230,000	230,000
Preferred stock, shares outstanding	230,000	230,000
Carrying value	230,000	230,000
Series C Fixed Rate Cumulative Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	151,500	151,500
Preferred stock, shares outstanding	151,500	151,500
Carrying value	$ 151,500	$ 151,500

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Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

+ 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 210.5-02.28)

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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29

-Article 5

+ Details

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- Definition

Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

+ References

+ Details

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- Definition

Aggregate par or stated value of issued nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer). This item includes treasury stock repurchased by the entity. Note: elements for number of nonredeemable preferred shares, par value and other disclosure concepts are in another section within stockholders' equity.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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 210.5-02.28)

-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 02

-Paragraph 29

-Article 5

+ Details

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