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Stockholders' Equity (Narrative) (Details) (USD $)
 1 Months Ended 12 Months Ended 1 Months Ended 12 Months Ended 12 Months Ended 1 Months Ended 12 Months Ended
Nov. 30, 2010
Mar. 31, 2012
Y
Mar. 31, 2011
Mar. 31, 2010
Mar. 31, 2012
Stock Options [Member]
Mar. 31, 2011
Stock Options [Member]
Mar. 31, 2010
Stock Options [Member]
May 31, 2011
Restricted Stock And Stock Awards [Member]
Mar. 31, 2012
Restricted Stock And Stock Awards [Member]
Mar. 31, 2011
Restricted Stock And Stock Awards [Member]
Mar. 31, 2010
Restricted Stock And Stock Awards [Member]
Mar. 31, 2012
Employee Stock Purchase Plan [Member]
Mar. 31, 2011
Employee Stock Purchase Plan [Member]
Mar. 31, 2010
Employee Stock Purchase Plan [Member]
Mar. 31, 2012
Performance-Based Restricted Stock [Member]
Mar. 31, 2012
2007 Plan [Member]
Mar. 31, 2012
2007 Director Plan [Member]
Nov. 30, 2010
Public Equity Offering [Member]
Mar. 31, 2012
Minimum [Member]
Stock Options [Member]
Mar. 31, 2012
Minimum [Member]
Restricted Stock And Stock Awards [Member]
Mar. 31, 2012
Minimum [Member]
U.S. Treasury Rates [Member]
Mar. 31, 2012
Maximum [Member]
Stock Options [Member]
Mar. 31, 2012
Maximum [Member]
Restricted Stock And Stock Awards [Member]
Mar. 31, 2012
Maximum [Member]
U.S. Treasury Rates [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]                                                
Shares issued in public equity offering                                   4,600,000            
Sale of common stock, price per share $ 35.50                                              
Proceeds from issuance of shares in public equity offering $ 155,200,000                                              
Underwriting costs and offering expenses 8,100,000                                              
Unrecognized compensation cost for unvested employee stock-based compensation awards outstanding, net of forfeitures         6,100,000 10,300,000     5,000,000 6,300,000                            
Weighted-average period over which unrecognized compensation expense is expected to be recognized (years)         1.9       1.7                              
Weighted-average grant-date fair value of stock option awards granted   $ 6.02 $ 17.43 $ 28.29                                        
Aggregate intrinsic value of exercisable options   8,400 8,700,000 16,400,000                                        
Aggregate intrinsic value of options exercised     13,000,000 11,400,000                                        
Average time period taken in calculating risk-free interest rate, years                                         5     7
Total fair value of restricted stock granted                 5,600,000 10,400,000 6,800,000                          
Total fair value of restricted stock vested                 4,100,000 5,500,000 8,400,000                          
Restricted stock granted   867,661                         109,211                  
Number of shares cancelled   157,926           20,250                                
Vesting period, in years                                     3 years 2 years   5 years 5 years  
Contractual life of options, in years   10                                            
Number of shares awarded annually                                 3,000              
Number of shares authorized for issuance under the plan                       439,204       1,608,057 198,000              
Compensation expense recognized                       100,000 100,000 100,000                    
Percentage of purchase discount                       15.00%                        
Common stock shares issued                       88,553                        
Stock-based compensation plans expired terms   May 2, 2007                                            
Stock-based compensation expense   $ 9,864,000 $ 13,412,000 $ 13,494,000 $ 6,177,000 $ 6,374,000 $ 5,895,000   $ 3,633,000 $ 6,919,000 $ 7,535,000 $ 54,000 $ 119,000 $ 64,000 $ (1,800,000)