Fair Value of Marketable Securities (Detail) - USD ($) $ in Millions |
Dec. 31, 2017 |
Dec. 31, 2016 |
---|---|---|
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ||
Trading Securities | $ 3.6 | $ 1.9 |
Fair Value, Inputs, Level 1 | ||
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ||
Trading Securities | 3.6 | 1.9 |
Fair Value, Inputs, Level 1 | Equity Funds | ||
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ||
Trading Securities | 2.1 | 1.1 |
Fair Value, Inputs, Level 1 | Fixed Income Funds | ||
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ||
Trading Securities | $ 1.5 | $ 0.8 |