Special Charges and Credits (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	0 Months Ended	9 Months Ended	24 Months Ended
Sep. 30, 2013 Third Quarter 2013 Secondary Offering [Member]	Jan. 31, 2012 January 25, 2012 Secondary Offering [Member]	Sep. 30, 2012 January 25, 2012 Secondary Offering [Member]	Dec. 31, 2012 January 25, 2012 Secondary Offering [Member]
Restructuring Cost and Reserve [Line Items]
Shares sold by certain stockholders in secondary offering (in shares)	12,070,920	12,650,000
Payments of stock issuance costs	$ 0.4		$ 0.5	$ 1.3
Stock issuance cost reimbursements				$ 0.6

The cash outflow for cost incurred directly with the issuance of an equity security.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 18, 19, 20

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3291-108585

Name:	us-gaap_PaymentsOfStockIssuanceCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration