Fair Value Measurements (Financial Assets Measured at Fair Value on a Recurring Basis) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	$ 218,543	$ 244,465
Cash Equivalents | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	23,038	10,680
Cash Equivalents | Corporate notes and bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	72,493	81,235
Short-term Investments | Corporate notes and bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	60,041	65,502
Short-term Investments | U.S. government agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	23,486	42,714
Short-term Investments | Restricted cash equivalents and investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	5,000	10,000
Available-for-sale Securities | Publicly Traded Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	34,485	34,334
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	57,145	76,447
Level 1 | Restricted cash equivalents and investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	0	0
Level 1 | Cash Equivalents | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	2	0
Level 1 | Cash Equivalents | Corporate notes and bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	0	0
Level 1 | Short-term Investments | Corporate notes and bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	0	0
Level 1 | Short-term Investments | U.S. government agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	22,658	42,113
Level 1 | Available-for-sale Securities | Publicly Traded Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	34,485	34,334
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	161,398	168,018
Level 2 | Restricted cash equivalents and investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	5,000	10,000
Level 2 | Cash Equivalents | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	23,036	10,680
Level 2 | Cash Equivalents | Corporate notes and bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	72,493	81,235
Level 2 | Short-term Investments | Corporate notes and bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	60,041	65,502
Level 2 | Short-term Investments | U.S. government agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	828	601
Level 2 | Available-for-sale Securities | Publicly Traded Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	0	0
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	0	0
Level 3 | Restricted cash equivalents and investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	0	0
Level 3 | Cash Equivalents | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	0	0
Level 3 | Cash Equivalents | Corporate notes and bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	0	0
Level 3 | Short-term Investments | Corporate notes and bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	0	0
Level 3 | Short-term Investments | U.S. government agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	0	0
Level 3 | Available-for-sale Securities | Publicly Traded Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	$ 0	$ 0