Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Mar. 31, 2014	Sep. 30, 2015
Schedule Of Allocation Of Income Tax Expense Benefit [Line Items]
Increase (decrease) in income tax expense benefit	$ 8.6		$ (3.1)
Changes in estimated jurisdictional mix of earnings	1.7	$ 5.6
Incremental benefit	$ 10.3
Federal research and development tax credit [Member]
Schedule Of Allocation Of Income Tax Expense Benefit [Line Items]
Incremental benefit		$ 2.5