Equity - Preferred Stock Terms (Detail) (USD $)	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012
8.5% Convertible perpetual preferred stock
Class of Stock
Preferred stock, dividend rate, percentage	8.50%	8.50%
Liquidation preference per share	$ 100.00
Annual dividend per share (in dollars per share)	$ 8.50
Conversion rate per share to common stock (in shares)	12.4805
Conversion date to common stock at Company's option	Feb. 20, 2014
6.0% Convertible perpetual preferred stock
Class of Stock
Preferred stock, dividend rate, percentage	6.00%	6.00%
Liquidation preference per share	$ 100.00
Annual dividend per share (in dollars per share)	$ 6.00
Conversion rate per share to common stock (in shares)	9.2115
Conversion date to common stock at Company's option	Dec. 21, 2014
7.0% Convertible perpetual preferred stock
Class of Stock
Preferred stock, dividend rate, percentage	7.00%	7.00%
Liquidation preference per share	$ 100.00
Annual dividend per share (in dollars per share)	$ 7.00
Conversion rate per share to common stock (in shares)	12.8791
Conversion date to common stock at Company's option	Nov. 20, 2015

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Number of shares issued for each share of convertible preferred stock that is converted.

+ References

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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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

The per share liquidation preference (or restrictions) of nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) that has a preference in involuntary liquidation considerably in excess of the par or stated value of the shares. The liquidation preference is the difference between the preference in liquidation and the par or stated values of the share.

+ 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=6928386&loc=d3e21475-112644

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21484-112644

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph d

-Article 4

Reference 5: 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.(d)(1))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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- Definition

Date the preferred stock has been redeemed, in CCYY-MM-DD format.

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+ Details

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