Share Based Compensation (Summary of Share Option Activity) (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Number of Common Shares
Balance at January 1, 2015	224,381
Granted	21,245
Exercised	(39,787)	(13,834)	(10,964)
Forfeited or expired	(71,708)
Balance at March 31, 2015	134,131	224,381
Exercisable, Common Shares	93,330
Weighted Average Exercise Share Price
Balance at January 1, 2015	$ 20.88
Granted	26.2
Exercised	15.12
Forfeited or expired	27.86
Balance at March 31, 2015	19.7	$ 20.88
Exercisable at December 31, 2014	17.45
Weighted average fair value of options granted during the year	$ 7.63	$ 8.05	$ 7.99
Weighted Average Contractual Remaining Life(Years)
Balance at end of period	3 years 3 months 18 days
Exercisable at end of period	2 years 2 months 12 days
Balance at January 1, 2015	$ 1,300
Exercised	458
Balance at March 31, 2015	974	$ 1,300
Exercisable, Intrinsic Value	$ 887