Description of the business and recent developments: Recent Accounting Pronouncements - to be adopted (Details) $ in Millions	Jan. 01, 2019 USD ($)
Cumulative effect adjustment \| ASU 2016-02
Recent accounting pronouncements- adopted
Asset and lease liability	$ 97.3

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration