Equity Investment	3 Months Ended
Mar. 31, 2018
Investments All Other Investments [Abstract]
Equity Investment	4. Equity Investment In March 2017, the Company participated in a Series B convertible preferred stock financing and invested $8.5 million in Viracta Therapeutics, Inc. (Viracta), a clinical stage drug development company. The Company did not exercise the option to purchase up to an additional $8.5 million worth of shares of the Series B convertible preferred stock by the expiration date of September 30, 2017. In May 2017, the Company executed an exclusive worldwide license with Viracta to develop and commercialize Viracta’s proprietary histone deacetylase inhibitor drug candidate for use in combination with NK cell therapy and possibly additional therapies. Based on the level of equity investment at risk, Viracta is not a Variable Interest Entity (VIE) and therefore is not consolidated under the VIE Model. Also, the Company does not hold a controlling financial interest in Viracta and therefore is not consolidating Viracta under the voting interest model. As the preferred stock is not considered in-substance common stock, the investment is not within the scope of accounting for the investment under the equity method. As the preferred stock does not have a readily determinable fair value, the Company has elected to apply the practicability exception noted under ASC 825 and estimates the fair value at its $8.5 million cost minus impairment, plus or minus changes resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer. As of March 31, 2018, the Company’s qualitative impairment assessment did not indicate there were events or changes in circumstances that may have had a significant adverse effect on the fair value of the investment. The Company has not recorded any impairments as of March 31, 2018 or on a cumulative basis. Further, the Company has not identified any downward or upward adjustments due to observable price changes in the investment as of the March 31, 2018 or on a cumulative basis. The $8.5 million cost of the investment is recorded in equity investment on the condensed consolidated balance sheet as of March 31, 2018.

4. Equity Investment

In March 2017, the Company participated in a Series B convertible preferred stock financing and invested $8.5 million in Viracta Therapeutics, Inc. (Viracta), a clinical stage drug development company. The Company did not exercise the option to purchase up to an additional $8.5 million worth of shares of the Series B convertible preferred stock by the expiration date of September 30, 2017. In May 2017, the Company executed an exclusive worldwide license with Viracta to develop and commercialize Viracta’s proprietary histone deacetylase inhibitor drug candidate for use in combination with NK cell therapy and possibly additional therapies.

Based on the level of equity investment at risk, Viracta is not a Variable Interest Entity (VIE) and therefore is not consolidated under the VIE Model. Also, the Company does not hold a controlling financial interest in Viracta and therefore is not consolidating Viracta under the voting interest model. As the preferred stock is not considered in-substance common stock, the investment is not within the scope of accounting for the investment under the equity method. As the preferred stock does not have a readily determinable fair value, the Company has elected to apply the practicability exception noted under ASC 825 and estimates the fair value at its $8.5 million cost minus impairment, plus or minus changes resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer.

As of March 31, 2018, the Company’s qualitative impairment assessment did not indicate there were events or changes in circumstances that may have had a significant adverse effect on the fair value of the investment. The Company has not recorded any impairments as of March 31, 2018 or on a cumulative basis. Further, the Company has not identified any downward or upward adjustments due to observable price changes in the investment as of the March 31, 2018 or on a cumulative basis. The $8.5 million cost of the investment is recorded in equity investment on the condensed consolidated balance sheet as of March 31, 2018.