Debt - Narrative (Detail) (USD $)
 1 Months Ended 3 Months Ended 12 Months Ended 1 Months Ended
Jul. 31, 2014
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Jun. 30, 2011
Jun. 30, 2008
Jun. 30, 2014
Dec. 31, 2013
Debt Instrument [Line Items]                
Other Assets, Fair Value Disclosure               $ 200,000
Loss on debt extinguishment       23,200,000        
Shares Issued with debt conversion 348,535              
Unamortized discount   30,655,000   32,256,000        
Long-term debt, net of discount   170,595,000   168,994,000        
Non-cash interest   1,883,000 2,528,000          
Issuance of common stock pursuant to conversion of debt 12,600,000              
5.375% Convertible Notes                
Debt Instrument [Line Items]                
Debt, interest rate           5.375%    
Debt, maturity date           Jun. 15, 2013    
Payments of long-term debt         85,100,000      
5.375% Convertible Notes | Investor                
Debt Instrument [Line Items]                
Unamortized discount         10,500,000      
Repurchase premium         21.50%      
3.75% Convertible Notes                
Debt Instrument [Line Items]                
Principal amount of Senior Notes         143,800,000      
Amount allocated to debt 27,900,000     140,300,000     112,400,000  
Amount allocated to equity 13,500,000           48,300,000  
Debt Instrument, Redemption, Principal Amount 300,000              
Repayment of remaining prinicpal amount including interest 300,000              
Debt, interest rate         3.75%      
Debt, maturity date         Jun. 15, 2016      
Debt Instrument, Repurchased Face Amount             114,900,000  
Frequency of interest payment         semi-annually      
Debt conversion rate         38.1749      
Principal amount per note used in conversion rate         1,000      
Conversion price, per share         $ 26.20      
Deferred financing costs, amortization period         5 years      
Payments of long-term debt             160,700,000  
Debt Instrument repurchase premium in dollars             45,800,000  
Principal Amount Of Old Debt Held             80,000,000  
Interest expense related to Notes   0 1,300,000          
Percentage required of the last reported sale price per share of the Company's common stock for redemption         130.00%      
Number of trading days         20 days      
Number of consecutive trading days         30 days      
Principal amount of debt converted 28,500,000              
Non-cash interest   0 2,800,000          
Total Consideration Paid 41,100,000              
3.75% Convertible Notes | Modified Debt                
Debt Instrument [Line Items]                
Unamortized discount         25,800,000      
Nonconvertible debt borrowing rate         16.50%      
Transaction fees         2,000,000      
3.75% Convertible Notes | Debt discount related to premium payment in connection with the purchase of                
Debt Instrument [Line Items]                
Unamortized discount         15,100,000      
3.75% Convertible Notes | Debt discount related to the increase in the value of the conversion feature.                
Debt Instrument [Line Items]                
Unamortized discount         200,000      
3.75% Convertible Notes | New Debt                
Debt Instrument [Line Items]                
Unamortized discount         26,600,000      
Nonconvertible debt borrowing rate         12.40%      
Debt discount amortization period         5 years      
Deferred financing costs         2,800,000      
Finance costs reclassified against equity         900,000      
Principal debt amount issued to new investors         84,300,000      
3.75% Convertible Notes | Semi Annual Payment, First Payment                
Debt Instrument [Line Items]                
Interest payment date         December 15      
3.75% Convertible Notes | Semi Annual Payment, Second Payment                
Debt Instrument [Line Items]                
Interest payment date         June 15      
2% Convertible Notes                
Debt Instrument [Line Items]                
Principal amount of Senior Notes   201,250,000   201,250,000     201,300,000  
Portion of 2% Notes purchased by 3.75% holders             98,200,000  
Debt, interest rate   2.00%         2.00%  
Debt, maturity date             Jun. 15, 2019  
Frequency of interest payment             semi-annually  
Debt conversion rate             21.5019  
Principal amount per note used in conversion rate             1,000  
Conversion price, per share             $ 46.51  
Unamortized discount   30,700,000            
Nonconvertible debt borrowing rate             6.20%  
Debt discount amortization period             5 years  
Finance costs reclassified against equity             1,200,000  
Deferred financing costs, amortization period             5 years  
Interest expense related to Notes   1,000,000            
Long-term debt, net of discount   170,600,000            
Non-cash interest   1,900,000            
Deferred Financing Costs, Gross             6,700,000  
2% Convertible Notes | Investor                
Debt Instrument [Line Items]                
Unamortized discount             35,600,000  
2% Convertible Notes | Semi Annual Payment, First Payment                
Debt Instrument [Line Items]                
Interest payment date             December 15  
2% Convertible Notes | Semi Annual Payment, Second Payment                
Debt Instrument [Line Items]                
Interest payment date             June 15  
Investor                
Debt Instrument [Line Items]                
Principal Amount Of Modified Debt Held         73,000,000      
Investor | 5.375% Convertible Notes                
Debt Instrument [Line Items]                
Principal amount of Senior Notes         70,000,000      
Principal Amount Of Modified Debt Held         13,500,000      
Investor | 3.75% Convertible Notes                
Debt Instrument [Line Items]                
Principal Amount Of Modified Debt Held         $ 59,500,000