Stockholders' Equity - Number of Shares (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 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	36,349	36,503	36,349	36,503
Effect of using weighted average common shares outstanding	54	78	(4)	125
Shares used in computing earnings per share-basic	36,403	36,581	36,345	36,628
Effect of shares issuable under stock option plans based on the treasury stock method	97	99	114	124
Effect of restricted and contingently issuable shares	66	57	74	69
Shares used in computing earnings per share-diluted	36,566	36,737	36,533	36,821