Contingencies and commitments (Details)	3 Months Ended
Mar. 31, 2013 2012 Settlement Qui Tam [Member] actions	Mar. 31, 2013 Additional Other Qui Tam [Member] actions	Dec. 19, 2012 Settled Litigation Related to Sales and Marketing Practices [Member] states
Loss Contingencies [Line Items]
Number of states			49
Number of claims settled/dismissed	1	2

The number of claims settled and dismissed during the period.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 9, 10, 11, 12

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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