Available for Sale Securities by Original Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Carrying Value
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less	$ 10,268	$ 8,683
Due greater than three years and less than five years	0	287
Total available-for-sale securities	10,268	8,970
Fair Value
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less	10,268	8,683
Due greater than three years and less than five years	0	287
Total available-for-sale securities	$ 10,268	$ 8,970