Stockholders' Equity - Number of Shares (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
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	36,042	36,400	36,042	36,400
Effect of using weighted average common shares outstanding	254	157	286	204
Shares used in computing earnings per share-basic	36,296	36,557	36,328	36,604
Effect of shares issuable under stock option plans based on the treasury stock method	73	125	100	124
Effect of restricted and contingently issuable shares	65	68	72	69
Shares used in computing earnings per share-diluted	36,434	36,750	36,500	36,797