Cash Cash Equivalents Short-Term Investments and Restricted Cash Equivalents and Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Cash and Cash Equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	$ 134,880	$ 163,200
Estimated Fair Value	134,879	163,198
Cash and Cash Equivalents | Cash
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	39,348	71,283
Estimated Fair Value	39,348	71,283
Cash and Cash Equivalents | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	23,038	10,680
Estimated Fair Value	23,038	10,680
Cash and Cash Equivalents | Corporate notes and bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	72,494	81,237
Estimated Fair Value	72,493	81,235
Short-term Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	83,483	108,119
Estimated Fair Value	83,527	108,216
Short-term Investments | Corporate notes and bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	60,005	65,426
Estimated Fair Value	60,041	65,502
Short-term Investments | U.S. government agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	23,478	42,693
Estimated Fair Value	23,486	42,714
Cash Cash Equivalents And Short Term Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	218,363	271,319
Estimated Fair Value	218,406	271,414
Restricted cash equivalents and investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	5,000	10,000
Estimated Fair Value	$ 5,000	$ 10,000