Stockholders' Equity - Number of Shares (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 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	36,503	36,854	36,503	36,854
Effect of using weighted average common shares outstanding	78	89	125	79
Shares used in computing earnings per share-basic	36,581	36,943	36,628	36,933
Effect of shares issuable under stock option plans based on the treasury stock method	99	221	124	226
Effect of restricted and contingently issuable shares	57	59	69	69
Shares used in computing earnings per share-diluted	36,737	37,223	36,821	37,228