Scheduled Maturities of Available-for-Sale Debt Securities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Due within one year, amortized cost	$ 1,280	$ 658
Due after one year through five years, amortized cost	1,198	1,415
Due after five years through 10 years, amortized cost	345	347
Total, amortized cost	2,823	2,420
Due within one year, fair value	1,292	659
Due after one year through five years, fair value	1,223	1,437
Due after five years through 10 years, fair value	346	346
Total, fair value	$ 2,861	$ 2,442