Investment Securities and Fair Value Measurements - Fair Value Measurements (Details) - Fair value measurements - USD ($)
$ in Thousands |
Mar. 31, 2018 |
Dec. 31, 2017 |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Total |
$ 59,368
|
$ 57,725
|
| Corporate bonds |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale - investment securities |
37,677
|
38,217
|
| Agency securities |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale - investment securities |
10,983
|
11,003
|
| Certificates of deposit |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale - investment securities |
1,984
|
2,981
|
| Treasury securities |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale - investment securities |
8,617
|
|
| Money market funds |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Cash equivalents |
107
|
5,524
|
| Level 1 |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Total |
10,708
|
8,505
|
| Level 1 | Corporate bonds |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale - investment securities |
0
|
0
|
| Level 1 | Agency securities |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale - investment securities |
0
|
0
|
| Level 1 | Certificates of deposit |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale - investment securities |
1,984
|
2,981
|
| Level 1 | Treasury securities |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale - investment securities |
8,617
|
|
| Level 1 | Money market funds |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Cash equivalents |
107
|
5,524
|
| Level 2 |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Total |
48,660
|
49,220
|
| Level 2 | Corporate bonds |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale - investment securities |
37,677
|
38,217
|
| Level 2 | Agency securities |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale - investment securities |
10,983
|
11,003
|
| Level 2 | Certificates of deposit |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale - investment securities |
0
|
0
|
| Level 2 | Treasury securities |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale - investment securities |
0
|
|
| Level 2 | Money market funds |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Cash equivalents |
0
|
0
|
| Level 3 |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Total |
0
|
0
|
| Level 3 | Corporate bonds |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale - investment securities |
0
|
0
|
| Level 3 | Agency securities |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale - investment securities |
0
|
0
|
| Level 3 | Certificates of deposit |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale - investment securities |
0
|
0
|
| Level 3 | Treasury securities |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale - investment securities |
0
|
|
| Level 3 | Money market funds |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Cash equivalents |
$ 0
|
$ 0
|