Summary of Significant Accounting Policies (Principles of Consolidation and Use of Estimates) (Details)	Dec. 31, 2017
Maximum
Schedule of Accounting Policies [Line Items]
Percentage of ownership recorded at cost	20.00%
Significant Influence
Schedule of Accounting Policies [Line Items]
Minimum percent of ownership to exercise significant influence	20.00%
Maximum percent of ownership to exercise significant influence	50.00%