Fair Value of Financial Instruments - Quantative Information About Unobservable Inputs (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2015	Dec. 31, 2016
Significant Unobservable Inputs (Level 3) | Minimum
IRLC - Loan closing rates	42.00%	43.00%
Significant Unobservable Inputs (Level 3) | Maximum
IRLC - Loan closing rates	99.00%	99.00%
IRLCs
IRLCs Fair Value	$ 787		$ 610
IRLCs | Quoted Prices in Active Markets for Identical Assets (Level 1)
IRLCs Fair Value	0		0
IRLCs | Significant Other Observable Inputs (Level 2)
IRLCs Fair Value	0		0
IRLCs | Significant Unobservable Inputs (Level 3)
IRLCs Fair Value	$ 787		$ 610
Other securities Valuation Technique	Discounted cash flow	Discounted cash flow
Other securities Unobservable Inputs	Loan closing rates	Loan closing rates
OREO | Significant Unobservable Inputs (Level 3)
IRLCs Fair Value	$ 648
Other securities Valuation Technique	Appraisal value
Other securities Unobservable Inputs	Marketability discount
Loan closing rates	24.00%