Long-Term Investments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	9 Months Ended
	Mar. 31, 2012 Investment	Sep. 30, 2013	Sep. 30, 2012
Investments Schedule [Abstract]
Number of long-term investments sold during the period	2
Auction rate securities sold, at par value	$ 4.0
Gain related to auction rate securities			0.3
Auction rate securities held, at par value		2.5
Maturity of long-term investment		2038
Recognized cumulative losses		0.5
Unrealized (losses) gains on auction rate securities		(0.2)	0.1
Cumulative unrealized gains		0.2
Carrying value of auction rate security		$ 2.0