Earnings per Common Share Reconciliation of Number of Common Shares Used in Calculating Basic and Diluted Net Earnings Per Share (Detail) - $ / shares		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Basic average common shares outstanding	[1]	17,531,703	19,334,729
Incremental shares due to:
Restricted stock units		48,033	55,734
Performance shares		23,396	74,306
Diluted average common shares outstanding		17,603,132	19,464,769
Basic net earnings per common share (in dollars per share)		$ 1.05	$ 0.30
Diluted net earnings per common share (in dollars per share)		$ 1.05	$ 0.30
Anti-dilutive shares excluded from calculation		710,062	399,452

[1] Basic average common shares outstanding include restricted stock awards that are fully vested, but are deferred for future issuance.