Stock Options - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 plan	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of incentive plans	2
Option vesting term	4 years
Unrecognized compensation cost related to stock option	$ 2.5
Weighted average period	2 years 9 months 18 days
Options vested	702,001
Weighted average exercise price	$ 18.46
Weighted average contractual term	4 years 7 months 6 days
Aggregate intrinsic value	8.0
Options exercisable	245,750	568,985	530,262
Options exercisable, Weighted average exercise price	$ 19.74	$ 21.46	$ 21.52
Option exercisable, Weighted average remaining contractual term	2 years 9 months 18 days
Option exercisable, aggregate intrinsic value	2.5
Cash received from the exercise of options	8.8	0	1.6
Tax benefits realized for the tax deductions from options exercised	1.4	0.3	0.3
Aggregate intrinsic value of stock options exercised	3.7	0.8	0.7
Total fair value of options expensed before tax benefits	$ 2.4	$ 2.3	$ 2.4
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of market value	100.00%
Stock options exercisable period maximum	10 years