Subsequent Event (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	0 Months Ended
Apr. 30, 2013
Subsequent events
Value of the entity's Class A Common Stock authorized to be repurchased	$ 90
Dividend Declared \| Class A Common Stock
Subsequent events
Quarterly dividend declared (in dollars per share)	$ 0.13
Dividend Declared \| Class B Common Stock
Subsequent events
Quarterly dividend declared (in dollars per share)	$ 0.13
Stock Repurchase Program
Subsequent events
Value of the entity's Class A Common Stock authorized to be repurchased	$ 90

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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