Available-for-Sale Securities Measured at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	$ 21,044	$ 45,992
Mutual funds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	2,058	2,023
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	9,893	29,737
Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	8,092	8,477
Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	1,001	5,755
Level 1
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities
Level 1 | Mutual funds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities
Level 1 | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities
Level 1 | Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities
Level 1 | Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities
Level 2
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	15,142	39,649
Level 2 | Mutual funds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	2,058	2,023
Level 2 | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	9,893	29,737
Level 2 | Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	2,190	2,134
Level 2 | Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	1,001	5,755
Level 3
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	5,902	6,343
Level 3 | Mutual funds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities
Level 3 | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities
Level 3 | Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	5,902	6,343
Level 3 | Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities