Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock-Based Compensation
Stock-based compensation expense	$ 5.0	$ 5.6	$ 4.8
Income tax benefit	$ 1.9	$ 2.1	1.8
Stock Options
Shares
Outstanding at beginning of year (in shares)	724
Granted (in shares)	102
Issuance of shares for options exercised including tax benefit (in shares)	(112)
Outstanding at end of year (in shares)	714	724
Options exercisable at end of year (in shares)	473
Weighted-Average Exercise Price
Outstanding at beginning of year (in dollars per share)	$ 14.69
Granted (in dollars per share)	30.36
Exercised (in dollars per share)	14.11
Outstanding at end of year (in dollars per share)	$ 17.01	$ 14.69
Other information
Intrinsic value of options exercised	$ 1.9	$ 3.9	$ 0.4
Weighted-average remaining contractual term of options exercisable	5 years 3 months 18 days
Aggregate intrinsic value of options exercisable	$ 9.2
Number of options that are vested and expected to vest (in shares)	700
Weighted average exercise price of options that are vested and expected to vest (in dollars per share)	$ 17.01
Weighted-average remaining contractual term of options that are vested and expected to vest	6 years 4 months 24 days
Aggregate intrinsic value of options that are vested and expected to vest	$ 11.6