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Short-term and Long-term Investments | 6 Months Ended
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Jun. 30, 2017
Investments, Debt and Equity Securities [Abstract] |
Short-term and Long-term Investments | Short-term and Long-term Investments The Company's investments are classified as available-for-sale. The following table summarizes the amortized cost, gross unrealized gains and losses, and fair value of available-for-sale investments as of June 30, 2017:
| Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Aggregate Fair Value
U.S. government debt securities | $ | 92,081 |  |  | $ | — |  |  | $ | (94 | ) |  | $ | 91,987 |
Corporate notes and bonds | 542 |  |  | — |  |  | — |  |  | 542 |
Certificates of deposit | 275 |  |  | — |  |  | — |  |  | 275 |
Total | $ | 92,898 |  |  | $ | — |  |  | $ | (94 | ) |  | $ | 92,804 |
The following table summarizes the amortized cost, gross unrealized gains and losses, and fair value of available-for-sale investments as of December 31, 2016:
| Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Aggregate Fair Value
U.S. government debt securities | $ | 180,412 |  |  | $ | 5 |  |  | $ | (94 | ) |  | $ | 180,323 |
Certificates of deposit | 272 |  |  | — |  |  | — |  |  | 272 |
Total | $ | 180,684 |  |  | $ | 5 |  |  | $ | (94 | ) |  | $ | 180,595 |
For more information on the Company's method for determining the fair value of its assets, see Note 2 – "Fair Value of Financial Instruments" in the Company's Annual Report on Form 10-K for the year ended December 31, 2016. As of June 30, 2017, all of the available-for-sale investments were due within one year based on their contractual maturities. Changes in market interest rates and bond yields cause certain investments to fall below their cost basis, resulting in unrealized losses on investments. The unrealized losses of the Company's investments were primarily a result of unfavorable changes in interest rates subsequent to the initial purchase of these investments and have been in a loss position for less than 12 months. As of June 30, 2017 and December 31, 2016, the Company did not consider any of its investments to be other-than-temporarily impaired. When evaluating its investments for other-than-temporary impairment, the Company reviews factors such as the length of time and extent to which fair value has been below its cost basis, the financial condition of the issuer, the Company's ability and intent to hold the security and whether it is more likely than not that it will be required to sell the investment before recovery of its cost basis.

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- Definition The entire disclosure for investments in certain debt and equity securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -URI http://asc.fasb.org/topic&trid=2196928 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 320 -URI http://asc.fasb.org/subtopic&trid=4738149 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -URI http://asc.fasb.org/subtopic&trid=2176304 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -URI http://asc.fasb.org/subtopic&trid=2324412 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -URI http://asc.fasb.org/subtopic&trid=2209399 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 954 -SubTopic 320 -URI http://asc.fasb.org/subtopic&trid=2289146 + Details
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