9. Retirement savings plan (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure Text Block Supplement [Abstract]
Defined Contribution Plan, Cost Recognized	$ 282,000	$ 265,000	$ 280,000

The amount of the cost recognized during the period for defined contribution plans.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

Name:	us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration