Summary of Share Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Number of Common Shares
Beginning Balance	635,197
Granted	20,633
Exercised	(1,217)	1,765
Forfeited or expired	(37,231)
Ending Balance	617,382
Exercisable at September 30, 2012	562,319
Weighted Average Exercise Share Price
Balance at January 1, 2012	$ 31.42
Granted	$ 19.02
Exercised	$ 12.84
Forfeited or expired	$ 31.95
Balance at September 30, 2012	$ 31.01
Exercisable at September 30, 2012	$ 32.27
Weighted average fair value of options granted during the year	$ 7.85	$ 7.76
Weighted Average Contractual Remaining Life(Years)
Balance at end of period	2 years
Exercisable at end of period	1 year 8 months 12 days
Aggregate Intrinsic Value
Balance at January 1, 2012	$ 406
Granted	5
Exercised	6
Forfeited or expired	30
Balance at September 30, 2012	551
Exercisable at September 30, 2012	$ 487