Properties and Equipment - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jul. 31, 2008	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Net proceeds received from sale-leaseback transactions	$ 35.8
Deferred gain on sale-leaseback transactions	$ 29.0	$ 10.6	$ 12.6
Lease period for sale-leaseback transactions	15 years
Rental expense		8.5	8.3	$ 7.2
Minimum future rental commitments		37.2
Minimum future rental commitments, year one		8.4
Minimum future rental commitments, year two		7.3
Minimum future rental commitments, year three		6.7
Minimum future rental commitments, year four		6.0
Minimum future rental commitments, year five		5.3
Minimum future rental commitments, thereafter		3.5
Other Current Liabilities [Member]
Property, Plant and Equipment [Line Items]
Deferred gain on sale-leaseback transactions		$ 1.9	$ 1.9