Fair Value Measurements (Financial Assets Measured at Fair Value on a Recurring Basis) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	$ 243,733	$ 153,352
Cash Equivalents | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	10,331	6,544
Cash Equivalents | Corporate notes and bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	83,473	20,697
Short-term Investments | Corporate notes and bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	68,178	39,254
Short-term Investments | U.S. government agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	34,868	39,485
Short-term Investments | Restricted cash equivalents and investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	10,064	10,168
Available-for-sale Securities | Publicly Traded Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	36,819	37,204
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	78,899	82,253
Level 1 | Cash Equivalents | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	0	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	32,016	34,881
Level 1 | Short-term Investments | Restricted cash equivalents and investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	10,064	10,168
Level 1 | Available-for-sale Securities | Publicly Traded Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	36,819	37,204
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	164,834	71,099
Level 2 | Cash Equivalents | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	10,331	6,544
Level 2 | Cash Equivalents | Corporate notes and bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	83,473	20,697
Level 2 | Short-term Investments | Corporate notes and bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	68,178	39,254
Level 2 | Short-term Investments | U.S. government agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	2,852	4,604
Level 2 | Short-term Investments | Restricted cash equivalents and investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value	0	0
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 | 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 | Short-term Investments | Restricted cash equivalents and investments
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