Stockholders' Equity-Number of Shares (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
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	37,134	37,230	37,134	37,230
Effect of using weighted average common shares outstanding	98	130	125	150
Shares used in computing earnings per share - basic	37,232	37,360	37,259	37,380
Effect of shares issuable under stock option plans based on the treasury stock method	293	319	312	331
Effect of restricted and contingently issuable shares	101	142	113	143
Shares used in computing earnings per share - diluted	37,626	37,821	37,684	37,854