Stock-Based Compensation - Restricted Stock Award and RSU Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted stock awards
Restricted stock, Shares Subject to Restriction
Outstanding at the beginning of the period (in shares)	172,506
Vested (in shares)	(82,924)
Forfeited (in shares)	(4,053)
Outstanding at the end of the period (in shares)	85,529	172,506
Restricted stock, Weighted Average Grant Date Fair Value
Outstanding at the beginning of the period (in dollars per share)	$ 19.37
Vested (in dollars per share)	18.17
Forfeited (in dollars per share)	22.46
Outstanding at the end of the period (in dollars per share)	$ 20.39	$ 19.37
Additional share-based compensation disclosures
Total fair value of shares vested	$ 2.3	$ 1.5	$ 1.0
Unrecognized pre-tax stock-based compensation expense	$ 1.1
Weighted average remaining service period	1 year 5 months 9 days
Restricted stock units
Restricted stock, Shares Subject to Restriction
Outstanding at the beginning of the period (in shares)	262,317
Granted (in shares)	488,552
Vested (in shares)	(67,057)	0	0
Forfeited (in shares)	(31,689)
Outstanding at the end of the period (in shares)	652,123	262,317
Restricted stock, Weighted Average Grant Date Fair Value
Outstanding at the beginning of the period (in dollars per share)	$ 22.32
Granted (in dollars per share)	26.55
Vested (in dollars per share)	22.27
Forfeited (in dollars per share)	22.81
Outstanding at the end of the period (in dollars per share)	$ 25.47	$ 22.32
Additional share-based compensation disclosures
Total fair value of shares vested	$ 2.0
Unrecognized pre-tax stock-based compensation expense	$ 13.2
Weighted average remaining service period	3 years 4 months 17 days
Minimum | Restricted stock awards
Additional share-based compensation disclosures
Period of service restrictions	1 year
Maximum | Restricted stock awards
Additional share-based compensation disclosures
Period of service restrictions	4 years