Share Based Compensation (Summary of Share Option Activity) (Detail) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Number of Common Shares
Balance at January 1, 2015	224,381
Granted	21,245
Exercised	(26,695)	(13,721)
Forfeited or expired	(71,708)
Balance at March 31, 2015	147,223
Exercisable, Common Shares	105,984
Weighted Average Exercise Share Price
Balance at January 1, 2015	$ 20.88
Granted	26.2
Exercised	14.68
Forfeited or expired	27.96
Balance at March 31, 2015	19.37
Exercisable at December 31, 2014	17.26
Weighted average fair value of options granted during the year	$ 7.63	$ 8.05
Weighted Average Contractual Remaining Life(Years)
Balance at end of period	3 years 8 months 12 days
Exercisable at end of period	2 years 8 months 12 days
Balance at January 1, 2015	$ 1,300
Exercised	308
Balance at March 31, 2015	1,268
Exercisable, Intrinsic Value	$ 1,137