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Related Party Transactions - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Related Party Transaction [Line Items]
Unfunded commitments	$ 0		$ 0		$ 2
Deposits from related parties	271,983		271,983		110,465
Aviation Time Sharing Agreement
Related Party Transaction [Line Items]
Payments to related party	36	$ 44	127	$ 267
Registration Rights Agreement \| 2016 IPO
Related Party Transaction [Line Items]
Payments to related party			671
Certain Executive Officers and Directors and Their Associates
Related Party Transaction [Line Items]
Unfunded commitments	10,852		10,852		4,672
Shareholders
Related Party Transaction [Line Items]
Unamortized leasehold improvements	121		121		137
Lease expense	128	$ 127	387	$ 377
Director \| Other Assets
Related Party Transaction [Line Items]
Amount of investment held by the company	$ 127		$ 127		$ 200