Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Net unrealized losses on investments	$ (8.6)	$ (4.2)
Net gains reclassified to revenue	$ 0.9	$ 7.2	$ 7.5