Share-Based Plans (Summary of Restricted Stock and Stock Option Activity) (Detail)	12 Months Ended
	Dec. 31, 2016 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options granted, Number of Shares	248,603
Options exercised, Number of Shares	292,304
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Restricted stock, Outstanding at beginning of period (in shares)	236,145
Restricted Stock, Granted (in shares)	248,418
Restricted stock, Vested restricted stock awards (in shares)	216,933	[1]
Restricted stock, Forfeited (in shares)	14,269
Restricted stock, Outstanding at end of period (in shares)	253,361
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Restricted stock, at beginning of period, Weighted-average Grant Date Fair Value (in dollars per share) | $ / shares	$ 32.58
Restricted stock, Granted (in dollars per share) | $ / shares	33.52
Restricted stock, Vested restricted stock awards (in dollars per share) | $ / shares	30.21	[1]
Restricted stock, Forfeited (in dollars per share) | $ / shares	32.89
Restricted stock, at end of period, Weighted-average Grant Date Fair Value (in dollars per share) | $ / shares	$ 32.24
Time Based Restricted Stock Unit Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Restricted stock, Outstanding at beginning of period (in shares)	2,088
Restricted Stock, Granted (in shares)	12,946
Restricted stock, Vested restricted stock awards (in shares)	12,876	[1]
Restricted stock, Forfeited (in shares)	0
Restricted stock, Outstanding at end of period (in shares)	2,158
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Restricted stock, at beginning of period, Weighted-average Grant Date Fair Value (in dollars per share) | $ / shares	$ 34.45
Restricted stock, Granted (in dollars per share) | $ / shares	32.89
Restricted stock, Vested restricted stock awards (in dollars per share) | $ / shares	33.23	[1]
Restricted stock, Forfeited (in dollars per share) | $ / shares	0.00
Restricted stock, at end of period, Weighted-average Grant Date Fair Value (in dollars per share) | $ / shares	$ 32.89
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Restricted stock, Outstanding at beginning of period (in shares)	115,721
Restricted Stock, Granted (in shares)	150,392
Restricted stock, Vested restricted stock awards (in shares)	140,531	[1]
Restricted stock, Forfeited (in shares)	9,398
Restricted stock, Outstanding at end of period (in shares)	116,184
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Restricted stock, at beginning of period, Weighted-average Grant Date Fair Value (in dollars per share) | $ / shares	$ 34.14
Restricted stock, Granted (in dollars per share) | $ / shares	32.75
Restricted stock, Vested restricted stock awards (in dollars per share) | $ / shares	33.12	[1]
Restricted stock, Forfeited (in dollars per share) | $ / shares	33.63
Restricted stock, at end of period, Weighted-average Grant Date Fair Value (in dollars per share) | $ / shares	$ 33.62
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding, at beginning of period, Number of Shares	1,527,074
Options granted, Number of Shares	0
Options exercised, Number of Shares	412,538
Options forfeited, Number of Shares	41,562
Options outstanding, at end of period, Number of Shares	1,072,974
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Options, at beginning of period, Weighted-average Exercise Price (in dollars per share) | $ / shares	$ 23.92
Options granted, Weighted-Average Exercise Price (in dollars per share) | $ / shares	0.00
Options exercised, Weighted-Average Exercise Price (in dollars per share) | $ / shares	28.47
Options forfeited, Weighted-Average Exercise Price (in dollars per share) | $ / shares	47.92
Options, at end of period, Weighted-average Exercise Price (in dollars per share) | $ / shares	$ 21.24

[1] Vested for purposes of recording compensation expense.