Quarterly report pursuant to Section 13 or 15(d)

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

v3.7.0.1
Share-Based Payments - Employee Activity Performance Shares (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense $ 2,064 $ 2,159 $ 4,026 $ 4,111
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) 76   80  
Grants in Period 0   25  
Additional Shares Awarded Based on Performance, Shares Issued in Period     0  
Shares Vested in Period     0  
Shares Forfeited in Period (4)   (33)  
Outstanding and non-vested, end of period (in shares) 72   72  
Outstanding and non-vested, weighted-average grant date fair value, beginning of period $ 57   $ 55  
Grants in Period, Weighted Average Grant Date Fair Value 0   56  
Stock Issued During Period, Weighted Average Grant Date Fair Value     0  
Vested in Period, Weighed-average grant date fair value     0  
Forfeited in Period, Weighted Average Grant Date Fair Value 56   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 $ 4,107   $ 4,107  
Share-based compensation expense 257 363 441 $ 714
Tax benefit related to share-based expense 94 135 160 266
Unrecognized share-based compensation, net of estimated forfeitures $ 2,135 $ 2,442 $ 2,135 $ 2,442
Weighted average period over which unrecognized compensation will be recognized (years) 2 years 11 days   2 years 11 days