Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Assets
Total assets	$ 4.1	$ 330.4
Liabilities
Total liabilities	1.1	1.5
Foreign Exchange Contract
Assets
Total assets	1.8	1.7
Liabilities
Total liabilities	1.1	1.5
Quoted prices in active markets for identical assets (Level 1)
Assets
Total assets	2.3
Significant Other Observable Inputs (Level 2)
Assets
Total assets	1.8	330.4
Liabilities
Total liabilities	1.1	1.5
Significant Other Observable Inputs (Level 2) | Foreign Exchange Contract
Assets
Total assets	1.8	1.7
Liabilities
Total liabilities	1.1	1.5
Available-for-Sale Securities
Assets
Total assets	2.3	328.7
Available-for-Sale Securities | Quoted prices in active markets for identical assets (Level 1)
Assets
Total assets	$ 2.3
Available-for-Sale Securities | Significant Other Observable Inputs (Level 2)
Assets
Total assets		$ 328.7