Annual report pursuant to Section 13 and 15(d)

Shareholders' Equity, Stock Options and Net Income per Share - Employee Activity - Performance Shares (Details)

v3.3.1.900
Shareholders' Equity, Stock Options and Net Income per Share - Employee Activity - Performance Shares (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Employee Activity - Performance Shares [Line Items]      
Share-based compensation $ 7,486 $ 6,681 $ 6,178
Key Employee Performance Share Based Plan [Member]      
Employee Activity - Performance Shares [Line Items]      
Share-based awards, vesting period 3 years    
Minimum percentage of peer group by which Company share price must outperform before incremental performance shares are issued 30.00%    
Percentage of Peer Group By Which Company Share Price Must Outperform Before Maximum Incremental Shares Are Issued 90.00%    
Outstanding at beginning of year (shares) 74 88 62
Granted (shares) 27 23 26
Additional shares awarded based on performance   19  
Vested (shares) (24) (56)  
Outstanding at end of year (shares) 77 74 88
Weighted average grant date fair value of non-vested shares at beginning of year $ 44 $ 37 $ 36
Weighted average fair value of performance shares 67 48 40
Stock Issued During Period, Weighted Average Grant Date Fair Value   30  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value 45 30  
Weighted average grant date fair value non-vested shares at end of year $ 52 $ 44 $ 37
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Total Fair Value $ 4,016 $ 3,279 $ 3,278
Share-based compensation 1,308 1,098 1,055
Tax benefit related to share-based compensation expense 512 $ 419 $ 402
Unrecognized compensation cost $ 1,726