Share-Based Plans (Summary of Restricted Stock and Stock Option Activity) (Detail)	6 Months Ended
	Jun. 30, 2017 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options exercisable, Number of Shares	840,558
Restricted Stock 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)	253,361
Restricted stock, Granted (in shares)	148,479
Restricted stock, Vested restricted stock awards (in shares)	106,532	[1]
Restricted stock, Forfeited (in shares)	12,344
Restricted stock, Outstanding at end of period (in shares)	282,964
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	$ 32.24
Restricted stock, Granted (in dollars per share) | $ / shares	55.53
Restricted stock, Vested restricted stock awards (in dollars per share) | $ / shares	35.26	[1]
Restricted stock, Forfeited (in dollars per share) | $ / shares	37.16
Restricted stock, at end of period, Weighted-average Grant Date Fair Value (in dollars per share) | $ / shares	$ 41.53
Restricted Stock Units (RSUs) [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)	2,158
Restricted stock, Granted (in shares)	8,129
Restricted stock, Vested restricted stock awards (in shares)	4,867	[1]
Restricted stock, Forfeited (in shares)	0
Restricted stock, Outstanding at end of period (in shares)	5,420
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	$ 32.89
Restricted stock, Granted (in dollars per share) | $ / shares	56.07
Restricted stock, Vested restricted stock awards (in dollars per share) | $ / shares	45.79	[1]
Restricted stock, Forfeited (in dollars per share) | $ / shares	0
Restricted stock, at end of period, Weighted-average Grant Date Fair Value (in dollars per share) | $ / shares	$ 56.07
Performance-Based Restricted Stock Awards 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)	116,184
Restricted stock, Granted (in shares)	89,581
Restricted stock, Vested restricted stock awards (in shares)	61,563	[1]
Restricted stock, Forfeited (in shares)	6,276
Restricted stock, Outstanding at end of period (in shares)	137,926
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	$ 33.62
Restricted stock, Granted (in dollars per share) | $ / shares	56.18
Restricted stock, Vested restricted stock awards (in dollars per share) | $ / shares	39.23	[1]
Restricted stock, Forfeited (in dollars per share) | $ / shares	42.72
Restricted stock, at end of period, Weighted-average Grant Date Fair Value (in dollars per share) | $ / shares	$ 45.42
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	1,072,974
Options granted, Number of Shares	0
Exercised options, Number of Shares	232,416
Options forfeited, Number of Shares	0
Options outstanding, at end of period, Number of Shares	840,558
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	$ 21.24
Options granted, Weighted-Average Exercise Price (in dollars per share) | $ / shares	0
Exercised options, Weighted-Average Exercise Price (in dollars per share) | $ / shares	27.97
Options forfeited, Weighted-Average Exercise Price (in dollars per share) | $ / shares	0
Options, at end of period, Weighted-average Exercise Price (in dollars per share) | $ / shares	$ 19.38

[1] ested for purposes of recording compensation expense.