Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock Repurchase Program
Total Shares Repurchased					500,000	400,000	400,000
Shares Repurchased Under Board Authorization					885,285	1,336,132	1,992,831
Total cost (in dollars)					$ 16.9	$ 22.1	$ 42.0
Average share price (in dollars per share)					$ 19.13	$ 16.55	$ 21.10
Shares withheld for net settlements of share-based awards, shares					531,346	391,195	418,135
Dividend Program
Dividend declared (in dollars per share)	$ 0.07	$ 0.07	$ 0.07	$ 0.07
Dividend paid (in dollars per share)	$ 0.07	$ 0.07	$ 0.07	$ 0.07
Aggregate cash dividends					$ 9.2
Aggregate stock dividends					$ 0.1
May 2013
Stock Repurchase Program
Number of shares authorized to repurchase by Board (in shares)	4,000,000				4,000,000
Total Shares Repurchased					4,000,000
Shares Repurchased Under Board Authorization							800,000
October 2014
Stock Repurchase Program
Number of shares authorized to repurchase by Board (in shares)	4,000,000				4,000,000
Total Shares Repurchased					3,400,000
Shares remaining under Board Authorization	600,000				600,000
Shares Repurchased Under Board Authorization					900,000	1,300,000	1,200,000