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Fair Value of Financial Instruments Fair Value Measurements and Disclosures (Details) - USD ($)
$ in Thousands
Dec. 31, 2019
Dec. 31, 2018
Fair Value    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure $ 31,824 $ 178,214
Liabilities, Fair Value Disclosure 3,613 4,728
Net Asset Fair Value 28,211 173,486
Fair Value | Significant Other Observable Inputs (Level 2)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 22,886 118,521
Liabilities, Fair Value Disclosure 3,089 3,364
Net Asset Fair Value 19,797 115,157
Fair Value | Significant Unobservable Inputs (Level 3)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 8,938 59,693
Liabilities, Fair Value Disclosure 524 1,364
Net Asset Fair Value 8,414 58,329
1.125% Convertible Senior Notes due 2021 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Notes fair value $ 188,600 $ 175,400
Notes fair value as percentage of par 94.30% 87.70%
6.125% Senior Notes due 2024 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Notes fair value $ 409,200 $ 370,200
Notes fair value as percentage of par 102.30% 92.50%
5.75% Senior Notes due 2026 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Notes fair value $ 599,400 $ 532,400
Notes fair value as percentage of par 99.90% 88.70%