Cash, Cash Equivalents and Investments - Cash, Cash Equivalents and Investments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Cash and Cash Equivalents [Line Items]
Amortized Cost	$ 20,093	$ 21,708
Fair Market Value	20,093	21,708
Short-term investments, Amortized Cost	6,838	8,264
Balance Per Balance Sheet	20,093	21,708	60,647	17,227
Short-term investments, Fair Market Value	6,848	8,272
Long-term investments, Amortized Cost	1,661	3,069
Short-term investments, Balance Per Balance Sheet	6,838	8,264
Long-term investments, Fair Market Value	1,665	3,080
Long-term investments, Balance Per Balance Sheet	1,661	3,069
Certificates of deposit [Member]
Cash and Cash Equivalents [Line Items]
Short-term investments, Amortized Cost	1,200	1,200
Short-term investments, Fair Market Value	1,200	1,200
Long-term investments, Amortized Cost	960	960
Short-term investments, Balance Per Balance Sheet	1,200	1,200
Long-term investments, Fair Market Value	962	962
Long-term investments, Balance Per Balance Sheet	960	960
Certificates of deposit [Member] | Minimum [Member]
Cash and Cash Equivalents [Line Items]
Short-term investments, Contracted Maturity	21 days	111 days
Long-term investments, Contracted Maturity	385 days	475 days
Certificates of deposit [Member] | Maximum [Member]
Cash and Cash Equivalents [Line Items]
Short-term investments, Contracted Maturity	200 days	290 days
Long-term investments, Contracted Maturity	438 days	528 days
Corporate debentures [Member]
Cash and Cash Equivalents [Line Items]
Long-term investments, Contracted Maturity	371 days
Short-term investments, Amortized Cost	4,938	5,667
Short-term investments, Fair Market Value	4,948	5,673
Long-term investments, Amortized Cost	701	2,109
Short-term investments, Balance Per Balance Sheet	4,938	5,667
Long-term investments, Fair Market Value	703	2,118
Long-term investments, Balance Per Balance Sheet	701	2,109
Corporate debentures [Member] | Minimum [Member]
Cash and Cash Equivalents [Line Items]
Short-term investments, Contracted Maturity	30 days	21 days
Long-term investments, Contracted Maturity		388 days
Corporate debentures [Member] | Maximum [Member]
Cash and Cash Equivalents [Line Items]
Short-term investments, Contracted Maturity	302 days	342 days
Long-term investments, Contracted Maturity		461 days
Cash [Member]
Cash and Cash Equivalents [Line Items]
Contracted Maturity	Demand	Demand
Amortized Cost	11,827	15,275
Fair Market Value	11,827	15,275
Balance Per Balance Sheet	11,827	15,275
Money market funds [Member]
Cash and Cash Equivalents [Line Items]
Contracted Maturity	Demand	Demand
Amortized Cost	8,266	6,433
Fair Market Value	8,266	6,433
Balance Per Balance Sheet	8,266	6,433
Commercial paper [Member]
Cash and Cash Equivalents [Line Items]
Short-term investments, Contracted Maturity	10 days
Short-term investments, Amortized Cost	700	1,397
Short-term investments, Fair Market Value	700	1,399
Short-term investments, Balance Per Balance Sheet	$ 700	$ 1,397
Commercial paper [Member] | Minimum [Member]
Cash and Cash Equivalents [Line Items]
Short-term investments, Contracted Maturity		52 days
Commercial paper [Member] | Maximum [Member]
Cash and Cash Equivalents [Line Items]
Short-term investments, Contracted Maturity		100 days