Fair Value Measurements and Marketable Securities - Marketable Securities with Unrealized Losses (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, in loss position for less than twelve months, Fair Value	$ 7,567
Marketable securities, in loss position for less than twelve months, Unrealized Loss	(7)
Government securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, in loss position for less than twelve months, Fair Value	1,118
Marketable securities, in loss position for less than twelve months, Unrealized Loss	(6)
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, in loss position for less than twelve months, Fair Value	6,449
Marketable securities, in loss position for less than twelve months, Unrealized Loss	$ (1)