XML 77 R63.htm IDEA: XBRL DOCUMENT v3.8.0.1
Common Stock (Details) - USD ($)
 1 Months Ended 12 Months Ended
Mar. 31, 2009
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2008
Equity, Class of Treasury Stock [Line Items]        
Common stock authorized by the Board of Directors (in shares) 1,200,000     2,250,000
Total purchased shares (in shares) 859,499 0 0  
Additional estimated shares (in shares)   207,756    
Closing price (in dollars per share)   $ 72.20    
Maximum [Member]        
Equity, Class of Treasury Stock [Line Items]        
Maximum percentage of repurchase of common stock 10.00%      
Bank credit agreement to permit share repurchases of common stock $ 15,000,000