Stock Compensation Plans - Unvested Stock Options and Activity (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Number of Stock Options
Outstanding at the beginning of the period (in shares)	194,126
Add: Options granted (in shares)	144,089
Less: Options vested (in shares)	115,201
Outstanding at the end of the period (in shares)	223,014
Weighted-Average Grant Date Fair Value
Outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 15.15
Add: Options granted (in dollars per share) | $ / shares	13.54
Less: Options vested (in dollars per share) | $ / shares	14.06
Outstanding at the end of the period (in dollars per share) | $ / shares	$ 13.87
Stock options.
Additional disclosures
Shares outstanding that vested and would have been exercisable had the participants reached retirement age	155,000
Aggregate grant date fair value of options subject to accelerated vesting | $	$ 2.1
Accelerated compensation expense (in dollars) | $	1.2
Aggregate grant date fair value of options vested, including options subject to accelerated vesting | $	$ 1.9