Quarterly report pursuant to Section 13 or 15(d)

Share-Based Payments - Employee Activity Performance Shares (Details)

v3.8.0.1
Share-Based Payments - Employee Activity Performance Shares (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense $ 1,939 $ 2,093 $ 5,965 $ 6,204
Key Employee Performance Share Based Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Period of Share Price Performance Comparison to Peer Group     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%  
Expected Stock Price Volatility Rate     24.70% 22.30%
Weighted Average Risk Free Interest Rate     1.40% 0.80%
Outstanding and non-vested, beginning of period (in shares) 72   80  
Grants in Period 1   26  
Shares Forfeited in Period (4)   (37)  
Outstanding and non-vested, end of period (in shares) 69   69  
Outstanding and non-vested, weighted-average grant date fair value, beginning of period $ 57   $ 55  
Grants in Period, Weighted Average Grant Date Fair Value 54   56  
Forfeited in Period, Weighted Average Grant Date Fair Value 57   51  
Outstanding and non-vested, weighted-average grant date fair value, end of period $ 57   $ 57  
Outstanding and non-vested, aggregate grant date fair value $ 3,956   $ 3,956  
Share-based compensation expense 249 367 689 $ 1,080
Tax benefit related to share-based expense 88 136 246 400
Unrecognized share-based compensation, net of estimated forfeitures $ 1,740 $ 2,076 $ 1,740 $ 2,076
Weighted average period over which unrecognized compensation will be recognized (years) 1 year 9 months 11 days   1 year 9 months 11 days