Financial Instruments (Bonds) - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Investments Debt And Equity Securities [Abstract]
Corporate and municipal bonds	$ 42.4	$ 40.8
Maturity dates of bonds, start date	2017-01
Maturity dates of bonds, end date	2021-12