Intangible Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Finite-lived intangible assets, gross carrying amount	$ 14.0	$ 14.0
Finite-lived intangible assets, accumulated amortization	10.8	9.8
Amortization expenses	$ 1.0	$ 1.1	$ 1.1