Loans - Defaults on Troubled Debt Restructurings (Details)	3 Months Ended	6 Months Ended					12 Months Ended
	Jun. 30, 2018 loan item	Jun. 30, 2018	Jun. 30, 2018 contract	Jun. 30, 2018 loan	Jun. 30, 2018 USD ($)	Jun. 30, 2017 item	Dec. 31, 2017 loan
Loans
Number of troubled debt restructurings in which the amount of principal or accrued interest owed from the borrower was forgiven | loan	0			0
Amounts that the company commits to lend customers with outstanding loans that are classified as troubled debt restructurings | $					$ 0
Number of loans modified as troubled debt restructurings during the period			3	0			0
Default period contractually past due under modified terms (in days)		30 days
Number of defaults on troubled debt restructurings | item	0					0
Period of consecutive payments (in months)		6 months