Stockholders' Equity - Number of Shares (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 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	36,894	37,187	37,209
Effect of using weighted average common shares outstanding	308	52	126
Shares used in computing earnings per share—basic	37,202	37,239	37,335
Effect of shares issuable under stock option plans based on the treasury stock method	283	316	330
Effect of restricted and contingently issuable shares	107	117	146
Shares used in computing earnings per share—diluted	37,592	37,672	37,811