Common Stock (Share-Based Compensation, Treasury Stock, and Stock Repurchase Plan) (Details) - USD ($)	12 Months Ended			31 Months Ended	62 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2017	Jun. 30, 2015	Nov. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-cash share-based compensation expense	$ 11,200,000	$ 12,100,000	$ 13,100,000
Common stock shares purchased as payment of income tax withholding (in shares)	199,644	238,216	473,304
Stock surrendered for exercise of stock options (in shares)	478,287	3,225	106,810
Common stock shares purchased, cost	$ 5,203,000		$ 9,697,000
Remaining authorized repurchase amount	49,700,000			$ 49,700,000	$ 49,700,000
Restated Revolving Credit, Term Loan and Security Agreement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share repurchase covenant	$ 9,700,000
Share Repurchase Program, November 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock repurchase shares authorized							$ 25,000,000
Common stock shares purchased by the company (in shares)	905,000	0	799,723
Common stock shares purchased, cost	$ 5,200,000		$ 9,700,000		$ 25,000,000
Common stock shares purchased, average cost per share (in dollars per share)	$ 5.75		$ 12.13
Share Repurchase Program, June 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock repurchase shares authorized						$ 50,000,000
Common stock shares purchased, cost				$ 300,000