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Stock-Based Compensation Plans (Details) - Restricted stock awards - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Stock-Based Compensation Plans    
Straight-line amortization period 4 years 2 months 12 days  
Unrecognized compensation cost $ 15.1  
Number of Shares    
Unvested at the beginning of the period (in shares) 929,000  
Unvested at the end of the period (in shares) 929,000  
Weighted-Average Grant-Date Fair Value    
Unvested at the beginning of the period (in dollars per share) $ 19.70  
Unvested at the end of the period (in dollars per share) $ 19.70  
General and administrative expenses    
Stock-Based Compensation Plans    
Stock-based compensation expense $ 0.9  
General and administrative expenses | Maximum    
Stock-Based Compensation Plans    
Stock-based compensation expense   $ 0.1