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Stock Repurchase Program (Details) - USD ($)
3 Months Ended 12 Months Ended 36 Months Ended
Nov. 03, 2014
Dec. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2017
Apr. 25, 2017
May 04, 2016
Class of Stock [Line Items]                
Repurchased Amount     $ 11,055,000 $ 5,390,000 $ 11,567,000      
Common Stock                
Class of Stock [Line Items]                
Number of Shares   788,416   319,805 711,708 1,819,929    
Repurchased Amount   $ 11,054,983   $ 5,390,355 $ 11,567,527 $ 28,012,865    
Average Price per Share   $ 14.02   $ 16.86 $ 16.25 $ 15.39    
15 Million Authorization, Expiring November 3, 2016 | Common Stock                
Class of Stock [Line Items]                
Stock repurchase program, authorized amount $ 15,000,000.0              
Stock Repurchase Program, Period in Force 24 months              
10 Million Authorization Expansion, Expiring May 4, 2018 | Common Stock                
Class of Stock [Line Items]                
Stock repurchase program, authorized amount               $ 10,000,000.0
Repurchased Amount     8,100,000          
15 Million Authorization, Expiring April 25, 2019 | Common Stock                
Class of Stock [Line Items]                
Stock repurchase program, authorized amount             $ 15,000,000.0  
Remaining authorized repurchase amount   $ 12,000,000.0 12,000,000.0     $ 12,000,000.0    
Repurchased Amount     $ 3,000,000.0