Summary of Share Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Number of Common Shares
Balance at January 1, 2013	440,453
Granted	20,229
Exercised	0
Forfeited or expired	(4,962)
Balance at March 31, 2013	455,720
Exercisable at March 31, 2013	410,185
Weighted Average Exercise Share Price
Balance at January 1, 2013	$ 29.17
Granted	$ 20.26
Exercised	$ 0.00
Forfeited or expired	$ 34.29
Balance at March 31, 2013	$ 28.72
Exercisable at March 31, 2013	$ 29.74
Weighted average fair value of options granted during the year		$ 7.85
Weighted Average Contractual Remaining Life(Years)
Balance at end of period	2 years 6 months
Exercisable at end of period	2 years
Aggregate Intrinsic Value
Balance at January 1, 2013	$ 557
Granted	0
Exercised	0
Forfeited or expired	0
Balance at March 31, 2013	651
Exercisable at March 31, 2013	$ 620