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Long-Term Debt - Additional Information (Detail)
1 Months Ended 3 Months Ended 12 Months Ended
Nov. 15, 2018
USD ($)
Aug. 20, 2018
USD ($)
$ / shares
Nov. 30, 2018
USD ($)
Dec. 31, 2018
USD ($)
$ / shares
Sep. 30, 2018
USD ($)
Jun. 30, 2018
USD ($)
Mar. 31, 2018
USD ($)
Dec. 31, 2018
USD ($)
$ / shares
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Debt Instrument [Line Items]                    
Conversion price (in dollars per share) | $ / shares       $ 101.38       $ 101.38    
Gain on sale of business       $ (9,072,000) $ 0 $ 0 $ 0 $ (9,072,000) $ 0 $ 0
Senior Notes | Convertible Note Due 2023                    
Debt Instrument [Line Items]                    
Principal amount   $ 316,300,000.0                
Interest rate (as a percent)   2.00%                
Conversion rate   9.8643                
Conversion price (in dollars per share) | $ / shares   $ 101.38                
Debt issuance costs   $ 8,400,000                
Interest expense               2,300,000    
Amortization of debt issuance costs               $ 3,000,000    
Effective interest rate       5.45%       5.45%    
Senior Notes | Convertible Notes 2023 Conversion Feature                    
Debt Instrument [Line Items]                    
Debt issuance costs   $ 7,200,000                
Senior Notes | 6% senior notes due 2022                    
Debt Instrument [Line Items]                    
Principal amount $ 300,000,000.0                  
Interest rate (as a percent) 6.00%                  
Redemption premium $ 6,000,000                  
Write off of deferred debt issuance cost $ 3,100,000                  
Line of Credit | Credit facility                    
Debt Instrument [Line Items]                    
Senior secured revolving line of credit       $ 550,000,000       $ 550,000,000    
Line of credit, maturity date               Jun. 26, 2020    
Debt issuance costs     $ 1,700,000              
Borrowings outstanding       0       $ 0    
Borrowing limit used       1,000,000       1,000,000    
Unamortized debt issue costs       $ 3,600,000       $ 3,600,000 $ 3,100,000  
Line of Credit | Credit facility | Minimum                    
Debt Instrument [Line Items]                    
Commitment fee (as a percent)               0.20%    
Fronting fees (as a percent)               1.25%    
Line of Credit | Credit facility | Minimum | London Interbank Offered Rate (LIBOR)                    
Debt Instrument [Line Items]                    
Basis spread (as a percent)     1.25%              
Line of Credit | Credit facility | Minimum | Base Rate                    
Debt Instrument [Line Items]                    
Basis spread (as a percent)     0.25%              
Line of Credit | Credit facility | Maximum                    
Debt Instrument [Line Items]                    
Commitment fee (as a percent)               0.35%    
Fronting fees (as a percent)               2.00%    
Line of Credit | Credit facility | Maximum | London Interbank Offered Rate (LIBOR)                    
Debt Instrument [Line Items]                    
Basis spread (as a percent)     2.00%              
Line of Credit | Credit facility | Maximum | Base Rate                    
Debt Instrument [Line Items]                    
Basis spread (as a percent)     1.00%              
Debt Instrument, Redemption, Period One | Senior Notes | Convertible Note Due 2023                    
Debt Instrument [Line Items]                    
Redemption price percentage               130.00%    
Debt Instrument, Redemption, Period Two | Senior Notes | Convertible Note Due 2023                    
Debt Instrument [Line Items]                    
Redemption price percentage               98.00%