12. Retirement Plan

        The Company has established a 401(k) plan for eligible employees to contribute up to 100% of their compensation, limited by the IRS-imposed maximum contribution amount. The Company matches 33% of each employee's contribution up to 6% of the employee's salary deferral. For the years ended December 31, 2015, 2014 and 2013, the Company made employer contributions of $0.8 million, $0.6 million and $0.4 million, respectively.