Assets Measured at Fair Value or Disclosed at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Assets
Total marketable securities	$ 13.8	$ 13.7
Corporate bonds
Assets
Total marketable securities	9.4	9.9
Exchange-traded funds
Assets
Total marketable securities	4.4	3.8
Fair Value, Inputs, Level 1
Assets
Total marketable securities	13.8	13.7
Fair Value, Inputs, Level 1 | Corporate bonds
Assets
Total marketable securities	9.4	9.9
Fair Value, Inputs, Level 1 | Exchange-traded funds
Assets
Total marketable securities	4.4	3.8
Fair Value, Inputs, Level 2
Assets
Total marketable securities	0	0
Fair Value, Inputs, Level 2 | Corporate bonds
Assets
Total marketable securities	0	0
Fair Value, Inputs, Level 2 | Exchange-traded funds
Assets
Total marketable securities	0	0
Fair Value, Inputs, Level 3
Assets
Total marketable securities	0	0
Fair Value, Inputs, Level 3 | Corporate bonds
Assets
Total marketable securities	0	0
Fair Value, Inputs, Level 3 | Exchange-traded funds
Assets
Total marketable securities	$ 0	$ 0