Short-term Investments - Amortized Cost and Estimated Fair Values of Short-Term Investments (Detail) (Certificates of deposit with maturities less than 1 year [Member], USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Certificates of deposit with maturities less than 1 year [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 12,684
Gross Unrealized Gains	1
Gross Unrealized Losses	(5)
Estimated Fair Value	$ 12,680