Employee Retirement Plans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Compensation expense	$ 1.7	$ 1.6	$ 1.1
Savings and Investment Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total expense for plans established pursuant to Section 401(k)	11.3	10.1	8.5
Hourly Tax-Sheltered Retirement Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total expense for plans established pursuant to Section 401(k)	$ 0.3	$ 0.3	$ 0.3
Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined contribution savings and investment plan, employees contribution rate	100.00%
First 3% of employee contributions
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer matching percentage of employee contributions	100.00%
The next 2% of employee contributions
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer matching percentage of employee contributions	50.00%