Common Stock, Maximum Aggregate Offering Price

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- Definition

Preferred Stock Dividend Rate, Basis Spread of Variable Rate

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No definition available.

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- Definition

Preferred Stock, Number of Series Outstanding

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No definition available.

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- Definition

Stock Repurchase Program Percentage Of Shares Repurchase Of Outstanding Share

+ References

No definition available.

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- Definition

The maximum percentage premium over the current book value for which stock can be repurchased.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Exercise price per share or per unit of warrants or rights outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(i)(4))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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- Definition

Number of warrants or rights outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(i))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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- Definition

The percentage rate used to calculate dividend payments on preferred stock.

+ References

No definition available.

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- Definition

Aggregate dividends paid during the period for each share of preferred stock outstanding.

+ References

No definition available.

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- Definition

Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

+ References

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- Definition

The price per share at which the preferred stock of an entity that has priority over common stock in the distribution of dividends and in the event of liquidation of the entity is redeemed or may be called at. The redemption features of this preferred stock are solely within the control of the issuer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21475-112644

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21564-112644

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21488-112644

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- Definition

Cash received on stock transaction after deduction of issuance costs.

+ References

No definition available.

+ Details

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- Definition

The number of shares issued or sold by the subsidiary or equity method investee per stock transaction.

+ References

No definition available.

+ Details

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- Definition

Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction.

+ References

No definition available.

+ Details

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- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

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- Definition

Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

+ 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 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(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644

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Shareholders' Equity - Narrative (Detail) $ / shares in Units, $ in Millions															12 Months Ended
	Dec. 15, 2017 $ / shares	Sep. 15, 2017 $ / shares	Jun. 15, 2017 $ / shares	Mar. 15, 2017 $ / shares	Dec. 15, 2016 $ / shares	Nov. 09, 2016 USD ($) $ / shares shares	Sep. 16, 2016 USD ($) $ / shares shares	Sep. 15, 2016 $ / shares	Aug. 11, 2016 USD ($) shares	Jun. 15, 2016 $ / shares	Apr. 28, 2016 USD ($) $ / shares shares	Mar. 15, 2016 $ / shares	Jan. 29, 2016 USD ($) $ / shares shares	May 18, 2015 USD ($) $ / shares shares	Dec. 31, 2017 series $ / shares shares	Dec. 31, 2016 $ / shares shares	Dec. 31, 2015 shares	Nov. 30, 2013
Capital Unit [Line Items]
Percent of outstanding shares authorized for repurchase																		5.00%
Premium percent over current book value																		20.00%
Stock repurchases (shares) \| shares															0	0	0
Warrants outstanding to purchase common stock (shares) \| shares															35,187	184,706
Share price															$ 21.38
Number of preferred stock series outstanding \| series															4
Preferred stock, par value (usd per share)															$ 1.00	$ 1.00
Minimum
Capital Unit [Line Items]
Purchase price of common stock (usd per share)															9.55	9.55
Maximum
Capital Unit [Line Items]
Purchase price of common stock (usd per share)															$ 73.01	$ 73.01
Series F Preferred Stock
Capital Unit [Line Items]
Preferred stock, dividends paid (usd per share)	$ 0.375	$ 0.375	$ 0.375	$ 0.375	$ 0.370833
Series E Preferred Stock
Capital Unit [Line Items]
Preferred stock, dividends paid (usd per share)	0.403125	0.403125	0.403125	0.403125	0.403125			$ 0.403125		$ 0.210521
Series D Preferred Stock
Capital Unit [Line Items]
Preferred stock, dividends paid (usd per share)	0.40625	0.40625	0.40625	0.40625	0.40625			0.40625		0.40625		$ 0.2076
Series C Preferred Stock
Capital Unit [Line Items]
Preferred stock, redemption price (usd per share)														$ 25.00
Preferred stock, dividends paid (usd per share)	$ 0.4375	$ 0.4375	$ 0.4375	$ 0.4375	$ 0.4375			$ 0.4375		$ 0.4375		$ 0.4375
Public Stock Offering
Capital Unit [Line Items]
Sale of stock, number of shares issued in transaction (shares) \| shares						2,415,000
Sale of stock, price per share (USD per share)						$ 25.00
Sale of stock, consideration received \| $						$ 58.3
Public Stock Offering \| Series F Preferred Stock
Capital Unit [Line Items]
Sale of stock, number of shares issued in transaction (shares) \| shares							3,400,000
Sale of stock, price per share (USD per share)							$ 25.00
Sale of stock, consideration received \| $							$ 82.2
Preferred stock, par value (usd per share)							$ 1.00
Preferred stock, fixed dividend rate							6.00%
Public Stock Offering \| Series F Preferred Stock \| London Interbank Offered Rate (LIBOR)
Capital Unit [Line Items]
Preferred stock, floating dividend rate							4.762%
Public Stock Offering \| Series E Preferred Stock
Capital Unit [Line Items]
Sale of stock, number of shares issued in transaction (shares) \| shares											2,300,000
Sale of stock, price per share (USD per share)											$ 25.00
Sale of stock, consideration received \| $											$ 55.6
Preferred stock, par value (usd per share)											$ 1.00
Preferred stock, fixed dividend rate											6.45%
Public Stock Offering \| Series E Preferred Stock \| London Interbank Offered Rate (LIBOR)
Capital Unit [Line Items]
Preferred stock, floating dividend rate											5.14%
Public Stock Offering \| Series D Preferred Stock
Capital Unit [Line Items]
Sale of stock, number of shares issued in transaction (shares) \| shares													1,000,000
Sale of stock, price per share (USD per share)													$ 25.00
Sale of stock, consideration received \| $													$ 24.1
Preferred stock, par value (usd per share)													$ 1.00
Preferred stock, fixed dividend rate													6.50%
Public Stock Offering \| Series D Preferred Stock \| London Interbank Offered Rate (LIBOR)
Capital Unit [Line Items]
Preferred stock, floating dividend rate													5.09%
Public Stock Offering \| Series C Preferred Stock
Capital Unit [Line Items]
Sale of stock, number of shares issued in transaction (shares) \| shares														2,300,000
Sale of stock, price per share (USD per share)														$ 25.00
Sale of stock, consideration received \| $														$ 55.6
Preferred stock, par value (usd per share)														$ 1.00
Preferred stock, fixed dividend rate														7.00%
Public Stock Offering \| Series C Preferred Stock \| London Interbank Offered Rate (LIBOR)
Capital Unit [Line Items]
Preferred stock, floating dividend rate														5.30%
At Market Issuance Sales Agreement
Capital Unit [Line Items]
Sale of stock, number of shares issued in transaction (shares) \| shares									219,386
Sale of stock, consideration received \| $									$ 5.5
Common stock, offering price \| $									$ 50.0