Number of stock bought back by the entity at the exercise price or redemption price.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 4, 5

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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_StockRedeemedOrCalledDuringPeriodShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Stock Repurchases (Details Textual) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2011 2008 Share Repurchase Plan [Member]	Mar. 31, 2013 2008 Share Repurchase Plan [Member]	Dec. 31, 2008 2008 Share Repurchase Plan [Member]	Mar. 31, 2013 2012 Share Repurchase Plan [Member]	Dec. 31, 2012 2012 Share Repurchase Plan [Member]
Equity, Class of Treasury Stock [Line Items]
Authorized amount for share repurchase	$ 400.0		$ 300.0		$ 300.0
Increase in authorized amount for share repurchase	100.0
Remaining authorized amount for share repurchase		$ 71.2
Shares repurchased		0		0