Long Term Obligations - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013
Debt Instrument [Line Items]
Total leverage ratio	1.01	1.01
Fixed charge coverage ratio	1.27	1.27
Line of Credit Facility Debt Restrictions	2.0	2.0
Maximum leverage ratio	2.0	2.0
Minimum fixed charge coverage ratio	1.25	1.25
Revolving Credit Facilities [Member]
Debt Instrument [Line Items]
Principal amount	$ 165.0	$ 165.0
Availability under the revolving credit facility	143.3	143.3
Outstanding letters of credit	21.7	21.7
Effective availability under the revolving credit facility	94.4	94.4
Term Loan [Member]
Debt Instrument [Line Items]
Term loan, period		5 years
Weighted-average interest rate for five year Term Loan	2.60%	2.70%
Principal amount	$ 60.0	$ 60.0