Equity Compensation Plans - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense	$ 0.7	$ 0.5	$ 2.0	$ 1.2
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	0	0	0	12,500
Cash received from exercise of stock option	0.7	0.3	1.6	1.2
Number of options exercised, intrinsic value	1.9	0.2	3.2	0.7
Employee Service Share-based Compensation, Tax Benefit Realized from Exercise of Stock Options	0.6		1.1	0.2
Stock Option Plan 2012 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share options and restricted shares authorized	1,750,000		1,750,000
Additional shares authorized under the plan			1,200,000
Time Based Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares granted	0		28,769	5,000
Performance Based Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares granted			138,000	84,790
Restricted shares Vested			64,200	61,800
Time Based Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares Vested			6,750
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation cost	3.5		3.5
Weighted average expected amortization period			2 years 3 months 18 days
Unvested restricted stock awards	410,664		410,664
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Exercised	92,050	30,074	183,267	128,060
Total unrecognized compensation cost	$ 1.1		$ 1.1
Weighted average expected amortization period			2 years 1 month 6 days