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Stock-Based Compensation (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended 91 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Jul. 01, 2019
Feb. 24, 2017
Jul. 11, 2011
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, Grants in Period 74,000   52,200        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value $ 2,000 $ 1,600 $ 1,100        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value $ 22.21 $ 0.00 $ 13.57        
Stock-based Compensation $ 1,285 $ 1,212 $ 1,134   $ 8,100    
Restricted Stock Shares Authorized             900,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized $ 500            
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price $ 18.36 $ 16.78 $ 13.81        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]              
Unvested at beginning of year, Number of Restricted Stock Awards (in shares) 53,000 102,400 183,100 211,500   44,584  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price $ 21.53 $ 18.36 $ 16.78 $ 13.81      
Share-based Compensation Arrangements by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period   17,900          
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value $ 17.27 $ 20.92 $ 25.40        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (122,200) (98,600) (75,600)        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value $ 16.21 $ 16.49 $ 14.34        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period (1,200) 0 (5,000)        
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition (in years) 1 year 3 months 26 days            
Maximum [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
weighted average fair value price of stock awards upper $ 18.78 $ 27.29 $ 27.47 18.18      
Minimum [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
weighted average fair value price of stock awards lower $ 17.06 $ 19.93 $ 21.72 $ 13.86