Loss per common share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Numerator [Abstract]
Net loss	$ (4,815)	$ (5,663)	$ 1,071	$ (5,649)	$ (11,760)	$ (13,668)	$ (3,305)	$ (7,937)	$ (15,056)	$ (36,670)	$ (11,930)
Denominator [Abstract]
Basic - weighted-average shares (in shares)									17,852,000	17,589,000	17,275,000
Effect of dilutive stock options (in shares)									0	0	0
Diluted - weighted-average shares (in shares)									17,852,000	17,589,000	17,275,000
Basic loss per common share (in dollars per share)	$ (0.27)	$ (0.32)	$ 0.06	$ (0.32)	$ (0.67)	$ (0.77)	$ (0.19)	$ (0.45)	$ (0.84)	$ (2.08)	$ (0.69)
Diluted loss per common share (in dollars per share)	$ (0.27)	$ (0.32)	$ 0.06	$ (0.32)	$ (0.67)	$ (0.77)	$ (0.19)	$ (0.45)	$ (0.84)	$ (2.08)	$ (0.69)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Options excluded from computation of earnings per share (in shares)									365,000	431,000	549,000