Shareholders' Equity and Equity Compensation (Time Based Restricted Stock Awards) (Detail) - Time Based Restricted Stock - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Awards Outstanding
Non-vested awards outstanding, beginning balance (in shares)	238,386	231,026	115,139
Awards granted (in shares)	75,160	93,780	156,665
Stock issued (in shares)	(93,813)	(62,378)	(12,436)
Awards forfeited or expired (in shares)	(11,415)	(24,042)	(28,342)
Non-vested awards outstanding, ending balance (in shares)	208,318	238,386	231,026
Weighted- Average Grant Date Fair Value
Weighted-Average Grant Date Fair Value, Outstanding at period beginning (in dollars per share)	$ 53.80	$ 48.54	$ 43.27
Weighted-Average Grant Date Fair Value, Awards granted (in dollars per share)	77.15	61.7	51.78
Weighted-Average Grant Date Fair Value, Stock issued (in dollars per share)	48.35	47.19	43.97
Weighted-Average Grant Date Fair Value, Awards forfeited or expired (in dollars per share)	61.32	51.19	47.07
Weighted-Average Grant Date Fair Value, Outstanding at period end (in dollars per share)	$ 64.27	$ 53.80	$ 48.54