XML 106 R93.htm IDEA: XBRL DOCUMENT v3.10.0.1
401(k) plan (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Retirement Benefits [Abstract]      
Matching contribution (as a percent of total salary) 92.00%    
Percentage of employee's base salary, matched by employer 6.00%    
Expense recorded $ 2.2 $ 1.6 $ 1.1