Fair Value Measurements (Financial Assets Measured at Fair Value on a Recurring Basis) (Detail) - USD ($) $ in Thousands | Sep. 30, 2017 | Dec. 31, 2016 |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | $ 62,619 | $ 80,525 |
Amortized Cost | 61,475 | 79,764 |
Cash and Cash Equivalents | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 45,597 | 33,721 |
Amortized Cost | 45,597 | 33,721 |
Cash and Cash Equivalents | Cash | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 27,254 | 32,585 |
Amortized Cost | 27,254 | 32,585 |
Cash and Cash Equivalents | Money market funds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 16,843 | 136 |
Amortized Cost | 16,843 | 136 |
Cash and Cash Equivalents | Corporate notes and bonds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 1,500 | 1,000 |
Amortized Cost | 1,500 | 1,000 |
Short-term Investments | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 13,482 | 43,331 |
Amortized Cost | 13,478 | 43,343 |
Short-term Investments | Corporate notes and bonds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 13,482 | 43,331 |
Amortized Cost | 13,478 | 43,343 |
Restricted cash equivalents and investments | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 2,400 | 2,700 |
Amortized Cost | 2,400 | 2,700 |
Related Party Transaction | Warrants issued by Rhapsody | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 1,140 | 773 |
Amortized Cost | 0 | 0 |
Level 1 | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 44,097 | 32,721 |
Level 1 | Cash and Cash Equivalents | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 44,097 | 32,721 |
Level 1 | Cash and Cash Equivalents | Cash | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 27,254 | 32,585 |
Level 1 | Cash and Cash Equivalents | Money market funds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 16,843 | 136 |
Level 1 | Cash and 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 | | |
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 | Restricted cash equivalents and investments | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 0 | 0 |
Level 1 | Related Party Transaction | Warrants issued by Rhapsody | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 0 | 0 |
Level 2 | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 17,382 | 47,031 |
Level 2 | Cash and Cash Equivalents | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 1,500 | 1,000 |
Level 2 | Cash and Cash Equivalents | Cash | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 0 | 0 |
Level 2 | Cash and Cash Equivalents | Money market funds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 0 | 0 |
Level 2 | Cash and Cash Equivalents | Corporate notes and bonds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 1,500 | 1,000 |
Level 2 | Short-term Investments | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 13,482 | 43,331 |
Level 2 | Short-term Investments | Corporate notes and bonds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 13,482 | 43,331 |
Level 2 | Restricted cash equivalents and investments | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 2,400 | 2,700 |
Level 2 | Related Party Transaction | Warrants issued by Rhapsody | | |
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 | 1,140 | 773 |
Level 3 | Cash and Cash Equivalents | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 0 | 0 |
Level 3 | Cash and Cash Equivalents | Cash | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 0 | 0 |
Level 3 | Cash and Cash Equivalents | Money market funds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 0 | 0 |
Level 3 | Cash and 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 | | |
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 | Restricted cash equivalents and investments | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 0 | 0 |
Level 3 | Related Party Transaction | Warrants issued by Rhapsody | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | $ 1,140 | $ 773 |