Fair Value Measurements (Financial Assets Measured at Fair Value on a Recurring Basis) (Detail) - USD ($) $ in Thousands | Jun. 30, 2018 | Dec. 31, 2017 |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | $ 44,952 | $ 63,364 |
Amortized Cost | 44,009 | 62,375 |
Cash and Cash Equivalents | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 39,080 | 51,196 |
Amortized Cost | 39,080 | 51,196 |
Cash and Cash Equivalents | Cash | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 21,538 | 31,065 |
Amortized Cost | 21,538 | 31,065 |
Cash and Cash Equivalents | Money market funds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 17,542 | 20,131 |
Amortized Cost | 17,542 | 20,131 |
Short-term Investments | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 3,053 | 8,779 |
Amortized Cost | 3,049 | 8,779 |
Short-term Investments | Corporate notes and bonds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 3,053 | 8,779 |
Amortized Cost | 3,049 | 8,779 |
Restricted cash equivalents | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 1,880 | 2,400 |
Amortized Cost | 1,880 | 2,400 |
Related Party Transaction | Warrants issued by Rhapsody | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 939 | 989 |
Amortized Cost | 0 | 0 |
Level 1 | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 39,080 | 51,196 |
Level 1 | Cash and Cash Equivalents | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 39,080 | 51,196 |
Level 1 | Cash and Cash Equivalents | Cash | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 21,538 | 31,065 |
Level 1 | Cash and Cash Equivalents | Money market funds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 17,542 | 20,131 |
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 | | |
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 | 4,933 | 11,179 |
Level 2 | Cash and Cash Equivalents | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 0 | 0 |
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 | Short-term Investments | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 3,053 | 8,779 |
Level 2 | Short-term Investments | Corporate notes and bonds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 3,053 | 8,779 |
Level 2 | Restricted cash equivalents | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Financial assets fair value | 1,880 | 2,400 |
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 | 939 | 989 |
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 | 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 | | |
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 | $ 939 | $ 989 |