Stockholders' Equity - Number of Shares (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
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	36,676	37,221	36,676	37,221
Effect of using weighted average common shares outstanding	129	73	215	15
Shares used in computing earnings per share-basic	36,805	37,294	36,891	37,236
Effect of shares issuable under stock option plans based on the treasury stock method	181	280	211	294
Effect of restricted and contingently issuable shares	65	93	68	104
Shares used in computing earnings per share-diluted	37,051	37,667	37,170	37,634