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Stock-Based Compensation (Details) (USD $)
 3 Months Ended 9 Months Ended 0 Months Ended 3 Months Ended 9 Months Ended 12 Months Ended 9 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2012
Dec. 31, 2011
Nov. 30, 2012
Stock options
Dec. 31, 2012
Stock options
Dec. 31, 2012
Stock options
Dec. 31, 2011
Stock options
Mar. 31, 2012
Stock options
Dec. 31, 2012
Stock options
Minimum
Dec. 31, 2011
Stock options
Minimum
Dec. 31, 2012
Stock options
Maximum
Dec. 31, 2011
Stock options
Maximum
Amounts recognized in the condensed financial statements related to stock-based compensation                          
Total cost of stock-based compensation charged against income before income taxes $ 459,000 $ 157,000 $ 897,000 $ 349,000                  
Amount of income tax benefit recognized in earnings 163,000 57,000 314,000 127,000                  
Amount charged against net income 296,000 100,000 583,000 222,000                  
Impact on net income per common share:                          
Basic (in dollars per share) $ 0.09 $ 0.03 $ 0.17 $ 0.07                  
Diluted (in dollars per share) $ 0.08 $ 0.03 $ 0.17 $ 0.06                  
Assumptions used to estimate the fair value of options granted                          
Volatility (as a percent)             29.30% 33.50%          
Risk-free interest rate, minimum (as a percent)             0.60% 0.90%          
Risk-free interest rate, maximum (as a percent)             1.00% 2.20%          
Expected option life                   5 years 5 years 10 years 10 years
Dividend yield (as a percent)             1.40% 1.80%          
Number of Shares                          
Outstanding at the beginning of the period (in shares)             433,785            
Options granted (in shares)             116,080            
Options forfeited (in shares)             (36,110)            
Options expired (in shares)             (40)            
Options exercised (in shares)             (63,375)            
Outstanding at the end of the period (in shares)           450,340 450,340   433,785        
Exercisable at the end of the period (in shares)           180,925 180,925            
Weighted-average Exercise Price per Share                          
Outstanding at the beginning of the period (in dollars per share)             $ 22.77            
Options granted (in dollars per share)             $ 50.01            
Options forfeited (in dollars per share)             $ 33.04            
Options expired (in dollars per share)             $ 18.98            
Options exercised (in dollars per share)             $ 20.17            
Outstanding at the end of the period (in dollars per share)           $ 29.33 $ 29.33   $ 22.77        
Exercisable at the end of the period (in dollars per share)           $ 21.30 $ 21.30            
Weighted- average Remaining Contractual Term                          
Outstanding                 3 years 10 months 24 days        
Options granted             6 years            
Exercisable at the end of the period             3 years            
Aggregate Intrinsic Value                          
Outstanding at the end of the period           9,392,000 9,392,000            
Exercisable at the end of the period           5,212,000 5,212,000            
Weighted average grant date fair value of option granted and intrinsic value of option exercised                          
Intrinsic value of options exercised             1,800,000 738,000          
Number of Shares                          
Unvested at the beginning of the period (in shares)             284,875            
Options granted (in shares)             116,080            
Options forfeited (in shares)             (36,110)            
Options vested (in shares)             (95,430)            
Unvested at the end of the period (in shares)           269,415 269,415   284,875        
Weighted-average Grant-Date Fair Value                          
Unvested at the beginning of the period (in dollars per share)             $ 7.23            
Options granted (in dollars per share)             $ 12.45            
Options forfeited (in dollars per share)             $ 8.97            
Options vested (in dollars per share)             $ 6.80            
Unvested at the end of the period (in dollars per share)           $ 9.40 $ 9.40   $ 7.23        
Unrecognized compensation cost                          
Unrecognized compensation cost           2,084,000 2,084,000            
Weighted average period of recognition             3 years            
Number of unvested options modified (in shares)         14,400                
Expiration term             10 years            
Incremental compensation expense           $ 240,000 $ 240,000