Stockholders' Equity - Number of Shares (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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	36,658	36,894	37,187
Effect of using weighted average common shares outstanding	196	308	52
Shares used in computing earnings per share-basic	36,854	37,202	37,239
Effect of shares issuable under stock option plans based on the treasury stock method	204	283	316
Effect of restricted and contingently issuable shares	73	107	117
Shares used in computing earnings per share-diluted	37,131	37,592	37,672