Capital Stock Capital Stock (Details) - USD ($)	12 Months Ended		57 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	May 23, 2016	Apr. 10, 2013
Capital Stock
Authorized shares of capital stock	105,000,000		105,000,000
Authorized shares of common stock	100,000,000	100,000,000	100,000,000
Common stock, par value (usd per share)	$ 0.01	$ 0.01	$ 0.01
Authorized shares of preferred stock	5,000,000	5,000,000	5,000,000
Preferred stock, par value (usd per share)	$ 0.001	$ 0.001	$ 0.001
Common stock reserved for future issuance (shares)	5,211,000		5,211,000
Common stock repurchased and retired, shares	775,370	230,163	1,640,012
Repurchase of common stock	$ 13,300,000	$ 4,000,000	$ 27,700,000
Average repurchase price per share (usd per share)	$ 17.16	$ 17.19
Number of shares remaining under Repurchase Programs	12,300,000		12,300,000
April 2013 Repurchase Program
Capital Stock
Common stock authorized for repurchase				$ 20,000,000	$ 20,000,000
Shares under the 2017 Stock Incentive Plan
Capital Stock
Common stock reserved for future issuance (shares)	4,967,000		4,967,000
Shares under the Amended and Restated 2009 Employee Stock Purchase Plan
Capital Stock
Common stock reserved for future issuance (shares)	244,000		244,000