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