Annual report pursuant to Section 13 and 15(d)

Cost Method Investments (Details)

v3.8.0.1
Cost Method Investments (Details) - Series A-1 - Convertible Preferred Stock - Compstak - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Aug. 31, 2016
Other assets      
Schedule of Cost-method Investments [Line Items]      
Cost method investments $ 3.0 $ 3.0  
Maximum      
Schedule of Cost-method Investments [Line Items]      
Cost method investment, ownership percentage (less than)     20.00%