Business and Summary of Significant Accounting Policies - Credit Quality Indicators (Details)	Dec. 31, 2018	Dec. 31, 2017
FICO Score, Less than 600
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Percentage of Loan Portfolio per FICO Score	3.70%	1.70%
FICO Score, 600 to 699
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Percentage of Loan Portfolio per FICO Score	77.90%	76.50%
FICO Score, Greater than 700
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Percentage of Loan Portfolio per FICO Score	18.40%	21.80%