Stock incentive plans (Details 5) (Unvested stock option, USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014
Unvested stock option
Stock incentive plans
Total stock-based compensation expense	$ 4,479
Weighted average period over which unrecognized compensation expense is expected to be recognized	2 years 1 month 10 days

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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Period Type:	duration