Common stock (Details) (USD $) In Millions, except Share data, unless otherwise specified							1 Months Ended			12 Months Ended
	Dec. 31, 2013 item	Dec. 31, 2012	Dec. 14, 2012	Dec. 31, 2011	Dec. 31, 2010	Apr. 30, 2011 Convertible notes issued in 2007 and 2008	Apr. 30, 2011 Common stock	Apr. 30, 2008 Common stock	Feb. 28, 2007 Common stock	Dec. 31, 2013 Common stock	Dec. 31, 2012 Common stock	Dec. 31, 2011 Common stock
Common stock
Number of votes to which holders of common shares are entitled for each share held at all general meetings	1
Number of common shares authorized	250,000,000	250,000,000	250,000,000	80,000,000	70,000,000
Number of preferred shares authorized	10,000,000	10,000,000	10,000,000	4,000,000	4,000,000
Common stock issued
Warrant exercises (in shares)										213,123	917,602	28,560
Employee option exercises (in shares)										304,769	488,513	267,573
Consideration shares upon acquisition of BPS (in shares)											488,337
April 2011 debt conversion (in shares)												4,474,776
Restricted stock grants (in shares)										860,739		915,000
Exercise of options and warrants (in shares)												296,133
Payment of accrued interest on convertible debt (in shares)							127,318
Other (in shares)												10,000
Total common stock issued										1,378,631	1,894,452	5,695,909
Additional disclosure
Debt instrument face amount						$ 9.0
Number of shares of common stock issued for convertible notes							4,049,776	1,333,333	2,272,727
Value of shares issued in lieu of cash payments for accrued interest							0.3
Shares issued in lieu of prepayment fee negotiated at the time conversion							297,682
Value of shares issued in lieu of prepayment fee negotiated at the time conversion							$ 0.6
Number of trading days period of which the average closing price of stock used for valuation of shares issued							10 days
Number of days prior to conversion not used for calculation of closing price of stock							2 days