Short-term Investments (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Schedule of Available-for-sale Securities [Line Items] | |||
| Available-for-sale securities, amortized cost | $ 19,403 | ||
| Available-for-sale securities, gross unrealized gains | 40 | ||
| Available-for-sale securities, gross unrealized losses | 0 | ||
| Available-for-sale securities, fair value | $ 19,443 | ||
| Investment Maturity Date | Dec. 31, 2017 | ||
| Available-for-sale Securities, Gross Realized Losses | $ 1 | $ 617 | $ 2,188 |
| Proceeds from Sale and Maturity of Marketable Securities | $ 43,232 | $ 82,115 | $ 182,115 |