Employee Benefit Plans - Options Outstanding by Exercise Price Range (Details) - Officer and Employee Plans [Member] - $ / shares	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices (in dollars per share)	$ 11.85	$ 10.57	$ 10.62
Number Outstanding (in shares)	187,316	717,524	817,414
Options Outstanding, Weighted Average Remaining Life	5 years 1 month 6 days
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 11.85
Options, Number Exercisable (in shares)	163,861
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 11.40
6.60 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices (in dollars per share)	$ 6.60
Number Outstanding (in shares)	38,250
Options Outstanding, Weighted Average Remaining Life	4 years 5 months 12 days
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 6.60
Options, Number Exercisable (in shares)	38,250
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.60
6.80 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices (in dollars per share)	$ 6.80
Number Outstanding (in shares)	16,875
Options Outstanding, Weighted Average Remaining Life	3 years 5 months 1 day
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 6.80
Options, Number Exercisable (in shares)	16,875
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.80
9.48 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices (in dollars per share)	$ 9.48
Number Outstanding (in shares)	26,875
Options Outstanding, Weighted Average Remaining Life	5 years 5 months 12 days
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 9.48
Options, Number Exercisable (in shares)	26,875
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 9.48
9.60 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices (in dollars per share)	$ 9.60
Number Outstanding (in shares)	35,625
Options Outstanding, Weighted Average Remaining Life	6 years 5 months 1 day
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 9.60
Options, Number Exercisable (in shares)	35,625
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 9.60
11.67 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices (in dollars per share)	$ 11.67
Number Outstanding (in shares)	2,000
Options Outstanding, Weighted Average Remaining Life	3 years 3 months 29 days
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 11.67
Options, Number Exercisable (in shares)	2,000
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 11.67
14.40 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices (in dollars per share)	$ 14.40
Number Outstanding (in shares)	12,805
Options Outstanding, Weighted Average Remaining Life	1 year 5 months 1 day
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 14.40
Options, Number Exercisable (in shares)	12,805
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 14.40
15.05 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices (in dollars per share)	$ 15.05
Number Outstanding (in shares)	41,720
Options Outstanding, Weighted Average Remaining Life	8 years 4 days
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 15.05
Options, Number Exercisable (in shares)	18,265
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 15.05
31.96 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices (in dollars per share)	$ 31.96
Number Outstanding (in shares)	13,166
Options Outstanding, Weighted Average Remaining Life	5 months 1 day
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 31.96
Options, Number Exercisable (in shares)	13,166
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 31.96