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Stock-Based Compensation (Narrative) (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based Payment Arrangement, Expense $ 3.5 $ 3.2 $ 10.4 $ 9.6
Nonvested Stock Award [Member] | Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period (in years)     4 years  
Nonvested Stock Award [Member] | Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period (in years)     7 years  
Stock Appreciation Rights (SARs) [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period (in years)     4 years  
Contractual terms of stock options granted (in years)     10 years