Quarterly report pursuant to Section 13 or 15(d)

Revenue (Major Customers) (Details)

v3.10.0.1
Revenue (Major Customers) (Details) - customer
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Major Customers        
Revenue as a percentage of the company's total 21.00% 20.00% 21.00% 20.00%
Revenues | Customer concentration risk | Fidelity        
Major Customers        
Number of customers accounted for as major customer 1 1 1 1
Revenue as a percentage of the company's total 16.00% 16.00% 16.00% 16.00%