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Employee Benefits Stock Based Incentive Plans (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock or Unit Option Plan Expense $ 437 $ 518 $ 653
Restricted Stock or Unit Expense 6,293 5,723 5,339
Allocated Share-based Compensation Expense 6,730 6,241 5,992
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense 2,574 2,367 2,311
Allocated Share-based Compensation Expense, Net of Tax $ 4,156 $ 3,874 $ 3,681
2009 Stock Option and Incentive Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized 4,000,000    
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant 2,700,968    
2010 Inducement Stock Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized 1,245,000    
Share-based Compensation Arrangement by Share-based Payment Award, Terms of Award The terms of the Inducement Plan are substantially similar to the terms of the 2009 Plan.    
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period 37,177 22,936 637,804
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant 148,854    
Employee Stock Purchase Plans [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Terms of Award Under the ESPP, eligible employees may purchase common stock of the Company at 85 percent of the lower of the closing price of the Company’s common stock on the first or last day of a six month purchase period on The NASDAQ® Global Select Market. Employees pay for their stock purchases through payroll deductions at a rate equal to any whole percentage from 1 percent to 15 percent of after-tax earnings.    
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period   165,919  
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant 777,726    
Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross 0    
Stock Options [Member] | 2009 Stock Option and Incentive Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Terms of Award Generally, options expire ten years from the date granted and vest over a three-year graded vesting period for officers and employees and a one-year or less period for non-employee directors.    
Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number 1,993,628 2,236,383  
Restricted Stock [Member] | 2009 Stock Option and Incentive Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Terms of Award Stock grants generally vest over a three-year cliff vesting period    
Performance Shares [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number 831,726    
Potential performance shares, incremental expense $ 8,100    
Potential Incremental Performance Shares Outstanding 665,381    
Maximum [Member] | Performance Shares [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number 1,497,107