Related Parties - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Notes Receivable Related Parties [Line Items]
Lease paid by company	$ 37.0	$ 35.7	$ 34.3
Director [Member]
Notes Receivable Related Parties [Line Items]
Lease paid by company	3.2	2.7	2.2
Akin Gump [Member]
Notes Receivable Related Parties [Line Items]
Legal charges paid	$ 0.1	$ 0.2	$ 0.6