Stock-Based Compensation - Fair Value Assumptions (Details) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) item $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares
Fair value assumptions:
Expected term		5 years 3 months 18 days	5 years 3 months 18 days
Additional information
Allocated Share-based Compensation Expense | $	$ 7.2	$ 6.4	$ 5.0
Stock Options
Stock-Based Compensation
Weighted-average fair value per share of options granted (in dollars per share)	$ 13.06	$ 11.43	$ 9.94
Fair value assumptions:
Expected dividend yield (as a percent)	0.79%	0.89%	0.97%
Expected stock price volatility (as a percent)	31.70%	34.50%	37.90%
Risk-free interest rate (as a percent)	2.66%	2.11%	1.41%
Expected term	5 years 3 months 18 days
Other information
Compensation expense yet to be recognized | $	$ 0.2
Weighted-average period over which compensation cost will be recognized	1 year 7 months 6 days
Total fair value of options vested | $	$ 0.9
Nonvested Options, Shares
Nonvested at beginning of year (in shares) | shares	186
Granted (in shares) | shares	87
Vested (in shares) | shares	(99)
Forfeited (in shares) | shares	(11)
Nonvested at end of year (in shares) | shares	163	186
Nonvested Options, Weighted-Average Grant Date Fair Value
Nonvested at beginning of year (in dollars per share)	$ 9.85
Granted (in dollars per share)	13.06	$ 11.43	$ 9.94
Vested (in dollars per share)	8.91
Forfeited (in dollars per share)	11.92
Nonvested at end of year (in dollars per share)	$ 11.99	$ 9.85
Additional information
Vesting period	3 years
Restricted Stock and Restricted Stock Units
Other information
Compensation expense yet to be recognized | $	$ 0.7
Weighted-average period over which compensation cost will be recognized	1 year 8 months 12 days
Shares
Unvested at beginning of year (in shares) | shares	92
Granted (in shares) | shares	69
Vested (in shares) | shares	(77)
Forfeited (in shares) | shares	(6)
Unvested at end of year (in shares) | shares	78	92
Weighted Average Grant Date Fair Value
Unvested at beginning of year (in dollars per share)	$ 30.48
Granted (in dollars per share)	44.02	$ 35.69	30.25
Vested (in dollars per share)	34.17
Forfeited (in dollars per share)	40.01
Unvested at end of year (in dollars per share)	$ 38.17	30.48
Additional information
Fair value of shares vested | $	$ 2.6
Weighted-average fair value (in dollars per share)	$ 44.02	$ 35.69	$ 30.25
Aggregate intrinsic value of restricted stock vested | $	$ 3.3	$ 3.2	$ 3.6
Performance Stock Units
Other information
Compensation expense yet to be recognized | $	$ 0.4
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 | $	$ 5.3
Value of PSUs granted | $	2.1
Allocated Share-based Compensation Expense | $	$ 2.9	$ 2.6	$ 1.6
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