Intrinsic Value of Options Exercised and Fair Value of Options Vested (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award Options Additional Disclosures [Abstract]
Intrinsic value of common stock options exercised	[1]	$ 0.1	$ 0.4	$ 0.1
Fair value of common stock options vested	[2]		$ 1.2	$ 0.8

[1] The intrinsic value of common stock options exercised is the difference between the fair value of the Company’s common stock on the exercise date and the exercise price.

[2] The fair value of common stock options vested is based on the grant date fair value.