Fair Value Measurements - Schedule of Financial Assets and Liabilities Measured at Fair Value (Detail) - USD ($)
$ in Thousands |
Mar. 31, 2018 |
Dec. 31, 2017 |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Total assets |
$ 44,542
|
$ 48,423
|
| Current Asset [Member] |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Total assets |
38,542
|
42,423
|
| Current Asset [Member] | Money Market Funds [Member] |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Cash equivalents |
3,072
|
2,014
|
| Restricted cash equivalents |
10,000
|
3,000
|
| Current Asset [Member] | Commercial Paper [Member] |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Cash equivalents |
16,476
|
16,477
|
| Current Asset [Member] | Corporate Bonds [Member] |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Cash equivalents |
1,507
|
1,457
|
| Current Asset [Member] | U.S. Government and Agency Securities [Member] |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Cash equivalents |
7,487
|
10,488
|
| Restricted cash equivalents |
|
8,987
|
| Non Current Assets [Member] |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Total assets |
6,000
|
6,000
|
| Non Current Assets [Member] | Money Market Funds [Member] |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Restricted cash equivalents |
6,000
|
6,000
|
| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Total assets |
26,559
|
30,489
|
| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Current Asset [Member] |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Total assets |
20,559
|
24,489
|
| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Current Asset [Member] | Money Market Funds [Member] |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Cash equivalents |
3,072
|
2,014
|
| Restricted cash equivalents |
10,000
|
3,000
|
| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Current Asset [Member] | U.S. Government and Agency Securities [Member] |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Cash equivalents |
7,487
|
10,488
|
| Restricted cash equivalents |
|
8,987
|
| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Non Current Assets [Member] |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Total assets |
6,000
|
6,000
|
| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Non Current Assets [Member] | Money Market Funds [Member] |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Restricted cash equivalents |
6,000
|
6,000
|
| Significant Other Observable Inputs (Level 2) [Member] |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Total assets |
17,983
|
17,934
|
| Significant Other Observable Inputs (Level 2) [Member] | Current Asset [Member] |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Total assets |
17,983
|
17,934
|
| Significant Other Observable Inputs (Level 2) [Member] | Current Asset [Member] | Commercial Paper [Member] |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Cash equivalents |
16,476
|
16,477
|
| Significant Other Observable Inputs (Level 2) [Member] | Current Asset [Member] | Corporate Bonds [Member] |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Cash equivalents |
$ 1,507
|
$ 1,457
|