Quarterly report pursuant to Section 13 or 15(d)

Share-Based Payments - Employee Activity Non-vested Shares (Details)

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Share-Based Payments - Employee Activity Non-vested 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
Employee Non-vested Shares [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Grants, vesting period (in years)     3 years  
Outstanding and non-vested, beginning of period (in shares) 232   222  
Stock Issued During Period, Shares, Restricted Stock Award, Gross 1   127  
Shares Vested in Period 0   (104)  
Shares Forfeited in Period (4)   (16)  
Outstanding and non-vested, end of period (in shares) 229   229  
Outstanding and non-vested, weighted-average grant date fair value, beginning of period $ 47   $ 45  
Grants in Period, Weighted Average Grant Date Fair Value 54   48  
Vested in Period, Weighed-average grant date fair value 0   45  
Forfeited in period (in dollars per share) 47   47  
Outstanding and non-vested, weighted-average grant date fair value, end of period $ 47   $ 47  
Outstanding and non-vested, aggregate grant date fair value $ 10,658   $ 10,658  
Share-based compensation expense 1,243 1,176 3,762 3,434
Tax benefit related to share-based expense 444 434 1,343 1,270
Unrecognized share-based compensation, net of estimated forfeitures $ 7,410 $ 7,147 $ 7,410 $ 7,147
Weighted average period over which unrecognized compensation will be recognized (years) 1 year 10 months 11 days   1 year 10 months 11 days