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Aggregate dividends declared during the period for each share of common stock outstanding.

+ 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=6959260&loc=d3e187085-122770

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- Definition

Date the declared dividend will be paid, in CCYY-MM-DD format.

+ References

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- Definition

Date the dividend to be paid was declared, in CCYY-MM-DD format.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 32

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format.

+ References

No definition available.

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Stockholders' Equity Common Stock (Detail) (USD $)	3 Months Ended								12 Months Ended
Stockholders' Equity Common Stock (Detail) (USD $)	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012 Dividend 1 [Member]	Dec. 31, 2012 Dividend 1 [Member] Common Stock [Member]	Dec. 31, 2012 Dividend 2 [Member]	Dec. 31, 2012 Dividend 2 [Member] Common Stock [Member]	Dec. 31, 2012 Dividend Three [Member]	Dec. 31, 2012 Dividend Three [Member] Common Stock [Member]	Dec. 31, 2012 Dividend Four [Member]	Dec. 31, 2012 Dividend Four [Member] Common Stock [Member]	Dec. 31, 2012 Dividend Five [Member]	Dec. 31, 2012 Dividend Five [Member] Common Stock [Member]	Dec. 31, 2012 Dividend Six [Member]	Dec. 31, 2012 Dividend Six [Member] Common Stock [Member]	Dec. 31, 2012 Dividend Seven [Member]	Dec. 31, 2012 Dividend Seven [Member] Common Stock [Member]	Dec. 31, 2012 Dividend Eight [Member]	Dec. 31, 2012 Dividend Eight [Member] Common Stock [Member]
Class of Stock [Line Items]
Declaration Date										Mar. 10, 2011		May 10, 2011		Aug. 04, 2011		Nov. 03, 2011		Feb. 28, 2012		May 03, 2012		Aug. 06, 2012		Nov. 01, 2012
Record date										Mar. 31, 2011		Jun. 30, 2011		Sep. 30, 2011		Dec. 31, 2011		Mar. 31, 2012		Jun. 29, 2012		Sep. 28, 2012		Dec. 31, 2012
Payment date										Apr. 12, 2011		Jul. 12, 2011		Oct. 12, 2011		Jan. 12, 2012		Apr. 12, 2012		Jul. 12, 2012		Oct. 12, 2012		Jan. 14, 2013
Dividend Amount	$ 0.40	$ 0.40	$ 0.40	$ 0.40	$ 0.40	$ 0.40	$ 0.40	$ 0.40	$ 0.40		$ 0.40		$ 0.40		$ 0.40		$ 0.40		$ 0.40		$ 0.40		$ 0.40