401(k) Plan	12 Months Ended
Dec. 31, 2017
Retirement Benefits [Abstract]
401(k) Plan	401(k) Plan In January 2005, we implemented a 401(k) Plan covering certain employees. Currently, all of our United States based employees over the age of 18 are eligible to participate in the 401(k) Plan. Under the 401(k) Plan, eligible employees may elect to reduce their current compensation up to a certain annual limit and contribute these amounts to the 401(k) Plan. We may make matching or other contributions to the 401(k) Plan on behalf of eligible employees. We recorded employer matching contributions expense of $0.6 million, $0.4 million and $0.5 million, respectively, in 2017, 2016 and 2015.

401(k) Plan

12 Months Ended

Dec. 31, 2017

In January 2005, we implemented a 401(k) Plan covering certain employees. Currently, all of our United States based employees over the age of 18 are eligible to participate in the 401(k) Plan. Under the 401(k) Plan, eligible employees may elect to reduce their current compensation up to a certain annual limit and contribute these amounts to the 401(k) Plan. We may make matching or other contributions to the 401(k) Plan on behalf of eligible employees. We recorded employer matching contributions expense of $0.6 million, $0.4 million and $0.5 million, respectively, in 2017, 2016 and 2015.