Share Repurchase Program (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Nov. 01, 2016	Dec. 31, 2011
Equity, Class of Treasury Stock [Line Items]
Amount available under the share repurchase program	$ 90,400,000
Purchase of treasury stock (in shares)	0	750,000
Treasury stock repurchased (in dollars per share)		$ 12.83
Purchase of treasury stock		$ 9,640,000
2016 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Authorized share repurchased program amount			$ 100,000,000
2011 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Amount available under the share repurchase program				$ 82,400,000