Fair Value Measurements - Fair Value of Investments in Marketable Securities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Equity securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Total investments		$ 19.6
Government bonds [Member]
Fair Value Of Other Financial Instrument [Line Items]
Total investments		72.1
Fair Value, Measurements, Recurring [Member]
Fair Value Of Other Financial Instrument [Line Items]
Total investments	95.3	91.7
Fair Value, Measurements, Recurring [Member] | Equity securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Total investments	14.7
Fair Value, Measurements, Recurring [Member] | Government bonds [Member]
Fair Value Of Other Financial Instrument [Line Items]
Total investments	$ 80.6