Summary of Available for Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities fair value	$ 17,282	$ 45,992
Available for sale securities Unrealized losses	(1,857)	(2,376)
Mutual funds
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities fair value	2,115	2,023
Available for sale securities Unrealized losses
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities fair value	7,397	29,737
Available for sale securities Unrealized losses
Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities fair value	7,770	8,477
Available for sale securities Unrealized losses	(1,857)	(2,376)
Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities fair value		5,755
Available for sale securities Unrealized losses