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Earnings Per Share (Details) - shares
shares in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Weighted Average Number of Shares Outstanding Reconciliation    
Weighted average number of common shares outstanding used to compute basic earnings per share 52,178 52,658
Dilutive effect of stock-based awards 653 591
Number of shares used to compute diluted earnings per share 52,831 53,249