Stock-Based Compensation Plans (Summary Of Stock Option Activity) (Detail) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Common Shares, Outstanding at beginning of the period (in shares)	1,698,912	1,551,734
Common Shares, Granted (in shares)	0	558,411
Common Shares, Exercised (in shares)	(374,046)	(99,760)
Common Shares, Forfeited or canceled (in shares)	(8,173)	(84,750)
Common Shares, Outstanding at end of the period (in shares)	1,316,693	1,925,635
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted Average Strike Price, Outstanding at beginning of period (usd per share)	$ 41.50	$ 41.32
Weighted Average Strike Price, Granted (usd per share)	0.00	40.96
Weighted Average Strike Price, Exercised (usd per share)	40.28	37.56
Weighted Average Strike Price, Forfeited or canceled (usd per share)	42.49	49.03
Weighted Average Strike Price, Outstanding at end of period (usd per share)	$ 41.84	$ 41.07
Stock Options, Exercisable (in shares)	765,711	896,155
Stock Options, Weighted Average Strike Price, Exercisable (usd per share)	$ 41.56	$ 39.08
Stock Options, Remaining Contractual Term, Outstanding, Years	4 years 4 months 24 days	4 years 10 months 24 days
Stock Options, Remaining Contractual Term, Exercisable, Years	3 years 8 months 12 days	3 years 7 months 6 days
Stock Options, Intrinsic Value, Outstanding	$ 45,561	$ 19,159
Stock Options, Intrinsic Value, Exercisable	$ 26,707	$ 10,695