Long Term Debt - Additional Information (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016	Sep. 30, 2017 USD ($)	Sep. 30, 2016	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Total leverage ratio	0.9		0.9
Fixed charge coverage ratio	4.1		4.1
Long-term debt including current portion	$ 89.9		$ 89.9		$ 93.0
Deferred debt issuance costs	(2.1)		(2.1)		(2.7)
Promissory Notes [Member]
Debt Instrument [Line Items]
Long-term debt including current portion	$ 0.7		$ 0.7		0.7
One Hundred Million Term Loan [Member]
Debt Instrument [Line Items]
Weighted-average interest rate for five year Term Loan	3.20%	2.50%	3.00%	2.50%
Principal amount	$ 100.0		$ 100.0
Maturity date			Aug. 28, 2020
Long-term debt including current portion	$ 91.3		$ 91.3		95.0
Two Hundred Million Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Weighted-average interest rate for five year Term Loan		4.50%		3.50%
Principal amount	$ 200.0		$ 200.0
Availability under the revolving credit facility	167.3		167.3
Outstanding letters of credit	32.7		$ 32.7
Maturity date			Aug. 28, 2020
Long-term debt including current portion	$ 0.0		$ 0.0		$ 0.0