|**Net Income Per Common Share**                                              | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
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|**Net Income Per Common Share [Abstract]**                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Net Income Per Common Share                                                  | Note 7 –Net Income per Common Share
		
		Basic net income per common share is based on the weighted average number of common shares outstanding.  Diluted net income per common share is based on the weighted average number of common shares outstanding and potentially dilutive shares.  The dilutive effect of employee stock-based compensation is included in the computation of diluted net income per common share.  The dilutive effect of stock-based compensation is calculated using the treasury stock method and expected proceeds upon exercise or issuance of the stock-based compensation.The treasury stock method assumes that the proceeds from the exercise of stock options are used to purchase the Company’s common stock at the average market price during the period.The following table summarizes the shares, in thousands, used in computing basic and diluted net income per common share:
		﻿
		﻿﻿﻿
				
				Three Months Ended﻿
				
				March 31,﻿
				
				2016
				
				2015﻿Average common shares outstanding during the period for basic computation
				
				177,104
				
				176,888﻿Dilutive effect of employee stock-based compensation
				
				715
				
				904﻿Average common shares outstanding during the period for diluted computation
				
				177,819
				
				177,792﻿
		﻿
		For the three months endedMarch 31, 2016 and 2015, all of the Company’s employee stock options were included in the calculations of diluted net income per share as the calculated cost to exercise the stock options was less than the average market price of the Company’s common stock during these periods.
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|﻿Average common shares outstanding during the period for basic computation   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|﻿Dilutive effect of employee stock-based compensation                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|﻿Average common shares outstanding during the period for diluted computation |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
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