Stockholders' Equity-Number of Shares (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 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	37,288	37,444	37,288	37,444
Effect of using weighted average common shares outstanding	8	(7)	(16)	(54)
Shares used in computing earnings per share - basic	37,296	37,437	37,272	37,390
Effect of shares issuable under stock option plans based on the treasury stock method	308	351	321	336
Effect of restricted and contingently issuable shares	101	123	121	144
Shares used in computing earnings per share - diluted	37,705	37,911	37,714	37,870