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Stockholders' Equity (Schedule of Stock Awards) (Details) - Stock Awards - $ / shares
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Number of Shares      
Balance at beginning of the period (in shares) 262,456 272,818 193,602
Granted (in shares) 86,918 96,010 103,500
Dividend equivalents (in shares) 3,811 8,992 7,675
Forfeited (in shares) (10,832) (16,534)  
Exercised (in shares) (109,731) (98,830) (31,959)
Balance at end of the period (in shares) 232,622 262,456 272,818
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]      
Outstanding exercise price (in usd per share) $ 49.36 $ 39.03 $ 30.84
Granted (in usd per share) $ 54.47 $ 60.29 $ 51.20
Dividend equivalents (in usd per share) 88.04 59.94 50.45
Forfeited (in usd per share) $ 53.95 $ 60.29  
Exercised (in usd per share) 39.94 29.70 26.88
Outstanding exercise price (in usd per share) $ 55.60 $ 49.36 $ 39.03