Common shares - Summary of Stock Options (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Equity [Abstract]
Outstanding, beginning of year, Shares	742,800	841,900
Granted, Shares	41,100	67,000
Forfeited, Shares	(160,150)	(98,100)
Exercised, Shares	(66,000)	(68,000)
Outstanding, ending of year, Shares	557,750	742,800
Exercisable, end of year, Shares	419,080	468,960
Outstanding, beginning of year, Weighted average exercise price	$ 11.80	$ 11.70
Granted, Weighted average exercise price	$ 6.51	$ 6.52
Forfeited, Weighted average exercise price	$ 12.67	$ 14.01
Exercised, Weighted average exercise price	$ 5.25	$ 2.20
Outstanding, end of year, Weighted average exercise price	$ 11.93	$ 11.80
Exercisable, end of year, Weighted average exercise price	$ 13.70	$ 14.44