Summary of Share Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Number of Common Shares
Beginning Balance	635,197
Granted	20,633
Exercised	(3,906)	2,037	30,498
Forfeited or expired	(211,471)
Ending Balance	440,453	635,197
Exercisable at December 31, 2012	386,037
Weighted Average Exercise Share Price
Beginning Balance	$ 31.42
Granted	$ 19.02
Exercised	$ 13.00
Forfeited or expired	$ 35.24
Balance at December 31, 2012	$ 29.17	$ 31.42
Exercisable at December 31, 2012	$ 30.73
Weighted average fair value of options granted during the year	$ 7.85	$ 7.76	$ 6.65
Weighted Average Contractual Remaining Life(Years)
Balance at end of period	2 years 6 months
Exercisable at end of period	2 years 1 month 6 days
Aggregate Intrinsic Value
Balance at January 1, 2012	$ 406
Granted	8
Exercised	23
Forfeited or expired	33
Balance at December 31, 2012	557	406
Exercisable at December 31, 2012	$ 484