Stock-Based Compensation - Fair Value Assumptions (Details) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) item $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares
Additional information
Allocated Share-based Compensation Expense | $	$ 6.4	$ 5.0	$ 5.6
Stock Options
Stock-Based Compensation
Weighted-average fair value per share of options granted (in dollars per share)	$ 11.43	$ 9.94	$ 6.33
Fair value assumptions:
Expected dividend yield (as a percent)	0.89%	0.97%	1.51%
Expected stock price volatility (as a percent)	34.50%	37.90%	38.40%
Risk-free interest rate (as a percent)	2.11%	1.41%	1.50%
Expected term	5 years 3 months 18 days	5 years 3 months 18 days	5 years 7 months 6 days
Other information
Compensation expense yet to be recognized | $	$ 0.4
Weighted-average period over which compensation cost will be recognized	1 year 4 months 24 days
Total fair value of options vested | $	$ 0.8
Nonvested Options, Shares
Nonvested at beginning of year (in shares) | shares	241
Granted (in shares) | shares	85
Vested (in shares) | shares	(117)
Forfeited (in shares) | shares	(23)
Nonvested at end of year (in shares) | shares	186	241
Nonvested Options, Weighted-Average Grant Date Fair Value
Nonvested at beginning of year (in dollars per share)	$ 7.83
Granted (in dollars per share)	11.43	$ 9.94	$ 6.33
Vested (in dollars per share)	7.23
Forfeited (in dollars per share)	7.88
Nonvested at end of year (in dollars per share)	$ 9.85	$ 7.83
Additional information
Vesting period	3 years
Restricted Stock and Restricted Stock Units
Other information
Compensation expense yet to be recognized | $	$ 0.8
Weighted-average period over which compensation cost will be recognized	1 year 7 months 6 days
Shares
Unvested at beginning of year (in shares) | shares	126
Granted (in shares) | shares	71
Vested (in shares) | shares	(90)
Forfeited (in shares) | shares	(15)
Unvested at end of year (in shares) | shares	92	126
Weighted Average Grant Date Fair Value
Unvested at beginning of year (in dollars per share)	$ 23.41
Granted (in dollars per share)	35.69	$ 30.25	20.64
Vested (in dollars per share)	25.44
Forfeited (in dollars per share)	26.34
Unvested at end of year (in dollars per share)	$ 30.48	23.41
Additional information
Fair value of shares vested | $	$ 2.3
Weighted-average fair value (in dollars per share)	$ 35.69	$ 30.25	$ 20.64
Aggregate intrinsic value of restricted stock vested | $	$ 3.2	$ 3.6	$ 3.4
Performance Stock Units
Other information
Compensation expense yet to be recognized | $	$ 0.7
Weighted-average period over which compensation cost will be recognized	1 year 2 months 12 days
Additional information
Vesting period	3 years
Types of performance units | item	2
Percentage of units measured on stock price relative to peer group	50.00%
Percentage of units measured on stock price based on pre determined EPS	50.00%
Period for which shareholder return is compared with peer group for units determined by EPS performance	3 years
Calculated fair market value | $	$ 4.9
Value of PSUs granted | $	2.2
Allocated Share-based Compensation Expense | $	$ 2.6	$ 1.6	$ 2.6
Performance Stock Units | Minimum
Additional information
Performance measures for dollar denominated award granted	0
Performance Stock Units | Maximum
Additional information
Performance measures for dollar denominated award granted	2.0