Cash, Cash Equivalents and Investments - Cash Equivalents and Level 1 Investments Measured at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total	$ 38,160	$ 38,102
Money market funds and other cash equivalents [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	631	4,500
Certificates of deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	6,493	5,062
U.S. government agency bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	8,576	8,498
Municipal bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	14,678	10,162
Corporate debt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	7,782	9,880
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total	7,124	9,562
Level 1 [Member] | Money market funds and other cash equivalents [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	631	4,500
Level 1 [Member] | Certificates of deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	6,493	5,062
Level 1 [Member] | U.S. government agency bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Level 1 [Member] | Municipal bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Level 1 [Member] | Corporate debt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total	31,036	28,540
Level 2 [Member] | Money market funds and other cash equivalents [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0	0
Level 2 [Member] | Certificates of deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Level 2 [Member] | U.S. government agency bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	8,576	8,498
Level 2 [Member] | Municipal bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	14,678	10,162
Level 2 [Member] | Corporate debt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	7,782	9,880
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total	0	0
Level 3 [Member] | Money market funds and other cash equivalents [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0	0
Level 3 [Member] | Certificates of deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Level 3 [Member] | U.S. government agency bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Level 3 [Member] | Municipal bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Level 3 [Member] | Corporate debt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	$ 0	$ 0