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Stockholders' Equity:Stock Repurchase (Details) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Feb. 25, 2015
Equity, Class of Treasury Stock [Line Items]        
Treasury Stock, Value, Acquired, Cost Method $ 4,930,000   $ 10,268,000  
ShareRepurchaseProgram2015 [Member]        
Equity, Class of Treasury Stock [Line Items]        
Stock Repurchase Program, Number of Shares Authorized to be Repurchased       2,000,000
Treasury stock, shares acquired 200,000 0 580,100  
Treasury Stock, Value, Acquired, Cost Method $ 4,900,000 $ 0 $ 10,300,000  
Treasury Stock Acquired, Average Cost Per Share $ 24.65   $ 17.70  
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased 496,989