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Summary of Significant Accounting Policies - (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) contract	Sep. 30, 2017 USD ($)
Disaggregation of Revenue [Line Items]
Number of active contracts \| contract			806,000
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	$ 24,500		$ 85,200
Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	4,700		14,500
Interchange and debit card transaction fees
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	2,300	$ 6,400	18,100	$ 19,600
Interchange and debit card transaction fees \| Before 606
Disaggregation of Revenue [Line Items]
Transaction fees	5,500	8,700	27,200	26,400
Network costs	3,200	2,300	9,100	6,800
Trust and investment services income
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	7,527	$ 6,310	22,608	$ 18,703
Deposit account services
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	$ 18,000		$ 63,700