Annual report pursuant to Section 13 and 15(d)

Major Customers (Details)

v3.8.0.1
Major Customers (Details) - customer
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Major Customers      
Revenue as a percentage of the company's total 22.00% 19.00% 18.00%
Revenues | Customer concentration risk | Fidelity      
Major Customers      
Number of customers accounted for as major customer 1 1 1
Revenue as a percentage of the company's total 17.00% 15.00% 18.00%