Investments

12 Months Ended

Dec. 31, 2017

Investments, All Other Investments [Abstract]

Investments

4.    Investments

Investments in Privately Held Companies

As of December 31, 2017 and 2016, we held non-marketable equity investments of approximately $36.1 million and $36.1 million, respectively, in privately held companies which are accounted for under the cost method. To date, we have not recognized any impairment losses on our investments.