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Borrowings - 2022 Notes - Additional Information (Detail) - USD ($)
1 Months Ended 12 Months Ended
Dec. 31, 2015
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Debt Instrument [Line Items]        
Debt maturity date   Jul. 15, 2020    
Interest expense   $ 34,650,000 $ 22,449,000 $ 18,769,000
Loss on extinguishment of debt   $ 5,202,000 14,566,000  
Change of Control Event [Member]        
Debt Instrument [Line Items]        
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest 101.00%      
Asset Sale Event [Member]        
Debt Instrument [Line Items]        
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest 100.00%      
2022 Notes [Member]        
Debt Instrument [Line Items]        
Aggregate principal amount $ 175,000,000     175,000,000
Net proceeds from the debt issuance 168,500,000      
Debt issuance costs 900,000      
Semi-annual installments of principal $ 21,875,000      
Debt maturity date Dec. 15, 2022      
Effective interest rate   12.32%    
Interest expense   $ 6,700,000 $ 20,900,000 $ 500,000
Loss on extinguishment of debt   25,000,000    
Prepayment penalty of extinguishment of debt   20,100,000    
Amortization expense recognized for remaining debt discount at settlement   4,900,000    
2022 Notes [Member] | Interest Expense [Member]        
Debt Instrument [Line Items]        
Loss on extinguishment of debt   $ 25,000,000    
2022 Notes [Member] | Conversion Terms, Fundamental Changes [Member]        
Debt Instrument [Line Items]        
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest     100.00%