Share-based Compensation Plans - Schedule of Changes in Restricted Stock (Detail)	12 Months Ended
	Dec. 31, 2015 $ / shares shares
Service-based Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Non-vested at the beginning of the period (in shares) | shares	374,926
Granted (in shares) | shares	203,618
Vested (in shares) | shares	(183,216)
Cancelled (in shares) | shares	(16,190)
Non-vested at the end of the period (in shares) | shares	379,138
Non-vested at the beginning of period (in dollars per share) | $ / shares	$ 30.47
Granted (in dollars per share) | $ / shares	33.27
Vested (in dollars per share) | $ / shares	30.35
Cancelled (in dollars per share) | $ / shares	27.42
Non-vested at the end of period (in dollars per share) | $ / shares	$ 32.15
Performance-based Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Non-vested at the beginning of the period (in shares) | shares	86,050
Granted (in shares) | shares	110,660
Cancelled (in shares) | shares	(4,400)
Non-vested at the end of the period (in shares) | shares	192,310
Non-vested at the beginning of period (in dollars per share) | $ / shares	$ 36.25
Granted (in dollars per share) | $ / shares	33.12
Cancelled (in dollars per share) | $ / shares	36.25
Non-vested at the end of period (in dollars per share) | $ / shares	$ 34.45