Fair Value Measurements - Summary of Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($)
$ in Thousands |
Dec. 31, 2015 |
Dec. 31, 2014 |
| Marketable securities: |
|
|
| Marketable securities |
$ 118,646
|
$ 184,757
|
| Money market mutual funds [Member] |
|
|
| Marketable securities: |
|
|
| Marketable securities |
1,038
|
1,919
|
| U.S. agency obligations [Member] |
|
|
| Marketable securities: |
|
|
| Marketable securities |
83,715
|
177,257
|
| U.S. treasury securities [Member] |
|
|
| Marketable securities: |
|
|
| Marketable securities |
33,893
|
5,581
|
| Fair Value, Measurements, Recurring |
|
|
| Marketable securities: |
|
|
| Assets, Fair Value Disclosure |
118,646
|
184,757
|
| Fair Value, Measurements, Recurring | Money market mutual funds [Member] |
|
|
| Cash equivalents: |
|
|
| Cash equivalents |
1,038
|
1,919
|
| Fair Value, Measurements, Recurring | U.S. agency obligations [Member] |
|
|
| Cash equivalents: |
|
|
| Cash equivalents |
3,000
|
1,561
|
| Marketable securities: |
|
|
| Marketable securities |
80,715
|
175,696
|
| Fair Value, Measurements, Recurring | U.S. treasury securities [Member] |
|
|
| Marketable securities: |
|
|
| Marketable securities |
33,893
|
5,581
|
| Fair Value, Measurements, Recurring | Level 1 [Member] |
|
|
| Marketable securities: |
|
|
| Assets, Fair Value Disclosure |
1,038
|
1,919
|
| Fair Value, Measurements, Recurring | Level 1 [Member] | Money market mutual funds [Member] |
|
|
| Cash equivalents: |
|
|
| Cash equivalents |
1,038
|
1,919
|
| Fair Value, Measurements, Recurring | Level 1 [Member] | U.S. agency obligations [Member] |
|
|
| Cash equivalents: |
|
|
| Cash equivalents |
0
|
0
|
| Marketable securities: |
|
|
| Marketable securities |
0
|
0
|
| Fair Value, Measurements, Recurring | Level 1 [Member] | U.S. treasury securities [Member] |
|
|
| Marketable securities: |
|
|
| Marketable securities |
0
|
0
|
| Fair Value, Measurements, Recurring | Level 2 [Member] |
|
|
| Marketable securities: |
|
|
| Assets, Fair Value Disclosure |
117,608
|
182,838
|
| Fair Value, Measurements, Recurring | Level 2 [Member] | Money market mutual funds [Member] |
|
|
| Cash equivalents: |
|
|
| Cash equivalents |
0
|
0
|
| Fair Value, Measurements, Recurring | Level 2 [Member] | U.S. agency obligations [Member] |
|
|
| Cash equivalents: |
|
|
| Cash equivalents |
3,000
|
1,561
|
| Marketable securities: |
|
|
| Marketable securities |
80,715
|
175,696
|
| Fair Value, Measurements, Recurring | Level 2 [Member] | U.S. treasury securities [Member] |
|
|
| Marketable securities: |
|
|
| Marketable securities |
$ 33,893
|
$ 5,581
|