Stockholders' Equity - Number of Shares (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of the number of shares outstanding with the number of shares used in computing basic and diluted earnings per share
Common shares outstanding, end of period	36,188	36,658	36,894
Effect of using weighted average common shares outstanding	354	196	308
Shares used in computing earnings per share-basic	36,542	36,854	37,202
Effect of shares issuable under stock option plans based on the treasury stock method	123	204	283
Effect of restricted and contingently issuable shares	73	73	107
Shares used in computing earnings per share-diluted	36,738	37,131	37,592