Stock-Based Compensation Plans (Summary Of Plans' Restricted Share And Performance-Vested Stock Award Activity) (Detail) - $ / shares	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Shares, Beginning of the Period	146,112	181,522
Shares, Granted	15,657	12,313
Shares, Vested and issued	(20,409)	(51,978)
Shares, Forfeited	(2,400)	(6,752)
Shares, Outstanding, End of the Period	138,960	135,105
Shares, Vested, but not issuable	85,000	85,000
Weighted Average Grant-Date Fair Value	$ 48.68	$ 47.09	$ 47.45	$ 43.39
Weighted Average Grant-Date Fair Value, Granted	45.81	46.04
Weighted Average Grant-Date Fair Value, Vested and issued	39.07	35.12
Weighted Average Grant-Date Fair Value, Forfeited	36.81	37.95
Weighted Average Grant-Date Fair Value, Vested, but not issuable	$ 51.88	$ 51.88
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Shares, Beginning of the Period	295,679	307,512
Shares, Granted	106,017	93,535
Shares, Vested and issued	(78,590)	(15,944)
Shares, Forfeited	(33,854)	(89,424)
Shares, Outstanding, End of the Period	289,252	295,679
Weighted Average Grant-Date Fair Value	$ 43.00	$ 38.18	$ 38.18	$ 34.01
Weighted Average Grant-Date Fair Value, Granted	44.35	46.85
Weighted Average Grant-Date Fair Value, Vested and issued	31.10	33.25
Weighted Average Grant-Date Fair Value, Forfeited	$ 32.74	$ 33.78