Contingencies and commitments (Details)	6 Months Ended
Jun. 30, 2013 2012 Settlement Qui Tam [Member] actions	Jun. 30, 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 pending claims		5
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 Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

Name:	us-gaap_LossContingencyClaimsSettledAndDismissedNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration