Stock-Based Compensation Restricted Stock Units (Details) - Restricted Stock Units (RSUs) [Member] - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$ 3.9	$ 4.7	$ 3.5
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Beginning balance	676,267
Units granted	249,011
Units vested	(207,306)
Units forfeited	(54,802)
Ending balance	663,170	676,267
Units Outstanding, Weighted Average Grant Date Fair Value	$ 17.75	$ 16.64
Units Granted, Weighted Average Grant Date Fair Value	20.11
Units vested during period, weighted average price	17.17
Units forfeited, Weighted Average Grant Date Fair Value	$ 16.92
RSUs weighted average contractual term	1 year 2 months
RSUs aggregate intrinsic value	$ 17,400,000
Fair Value of Awards vested during period	$ 4.5	$ 2.4	$ 5.4
Unrecognized compensation costs	$ 4.1