Subsequent Events (Details) (USD $)	12 Months Ended	0 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jan. 31, 2013 Dividend Declared [Member]
Subsequent Event [Line Items]
Dividends declared per share	$ 0.6400	$ 0.4775	$ 0.4325	$ 0.1725
Dividends payable per share				$ 0.1725

The per share amount of a dividend declared, but not paid, as of the financial reporting date.

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

Name:	us-gaap_DividendsPayableAmountPerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant