Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) plan $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of incentive plans | plan	2
Options, Granted (in shares) | shares	129,400
Weighted-average fair value of grants (in dollars per share) | $ / shares	$ 11.88
Outstanding at end of period, Weighted average remaining contractual term	5 years 2 months 12 days
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, Granted (in shares) | shares	129,400	123,500	73,000
Weighted-average fair value of grants (in dollars per share) | $ / shares	$ 11.88	$ 6.53	$ 10.63
Expiration period from date of grant	7 years
Option vesting term	4 years
Aggregate intrinsic value of stock options exercised	$ 2.5	$ 1.3	$ 2.3
Cash received from the exercise of options	4.3	2.1	3.1
Tax benefits realized for the tax deductions from options exercised	$ 0.9	0.5	0.9
Options vested (in shares) | shares	306,225
Weighted average exercise price (in dollars per share) | $ / shares	$ 23.38
Aggregate intrinsic value	$ 1.7
Outstanding at end of period, Weighted average remaining contractual term	5 years 2 months 12 days
Share-based compensation expense	$ 0.7	0.8	1.2
Unrecognized compensation cost related to stock option	$ 1.5
Weighted average period	3 years 1 month 6 days
Total fair value of options expensed before tax benefits	$ 0.8	0.9	1.3
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option vesting term	3 years
Share-based compensation expense	$ 2.0	$ 1.8	$ 1.8
Weighted average period	2 years
Awards, Granted (in shares) | shares	135,350	139,450	108,500
Weighted average grant date fair value (in dollars per share) | $ / shares	$ 28.97	$ 15.97	$ 25.15
Vesting percentage in year one	33.00%
Vesting percentage in year two	33.00%
Vesting percentage in year three	34.00%
Compensation not yet recognized	$ 3.0
Fair value of awards vested in period	3.0	$ 1.3	$ 1.8
Tax benefit realized on vesting of options	1.1	0.7	0.7
Performance Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 2.0	$ 0.4	$ 0.5
Weighted average period	1 year 8 months 12 days
Awards, Granted (in shares) | shares	126,000	62,500	64,000
Weighted average grant date fair value (in dollars per share) | $ / shares	$ 26.31	$ 15.92	$ 25.51
Compensation not yet recognized	$ 2.4
Fair value of awards vested in period	1.2	$ 1.1	$ 0.9
Tax benefit realized on vesting of options	$ 0.5	$ 0.2	$ 0.3
2007 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares) | shares	1,200,000
Shares reserved for future issuance other than stock options | shares	400,000
Shares reserved for future issuance | shares	0
2013 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares) | shares	1,040,000
Shares reserved for future issuance | shares	77,693