Summary of Significant Accounting Policies - Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 02, 2018	Dec. 31, 2017
Other Accrued Liabilities
Accrued contract payments	$ 6,389		$ 4,901
Accrued clinical trial costs	11,087		8,400
Accrued professional services	1,171		723
Accrued employee benefits	651		574
Accrued public reporting charges	164		156
Other current accrued liabilities	1,003		1,013
Total	20,465	$ 15,767	15,767
Deferred revenue, net of current portion	80,485	$ 88,521	93,752
Technological Improvements
Other Accrued Liabilities
Deferred revenue, net of current portion	$ 5,900		$ 6,800