Stockholders' Equity - Number of Shares (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
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	36,400	36,676	36,400	36,676
Effect of using weighted average common shares outstanding	157	129	204	215
Shares used in computing earnings per share-basic	36,557	36,805	36,604	36,891
Effect of shares issuable under stock option plans based on the treasury stock method	125	181	124	211
Effect of restricted and contingently issuable shares	68	65	69	68
Shares used in computing earnings per share-diluted	36,750	37,051	36,797	37,170