Annual report pursuant to Section 13 and 15(d)

Debt (Interest Expense) (Details)

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Debt (Interest Expense) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Debt Instrument [Line Items]      
Total interest expense $ 14,534 $ 8,994 $ 8,244
Convertible Notes, Credit and Amended and Restated Credit Agreements      
Debt Instrument [Line Items]      
Coupon interest 6,650 3,019 3,019
Amortization of issuance costs 2,771 3,279 2,875
Accretion of debt discount 11,134 5,472 5,237
Interest on credit agreement 3,994 4,153 5,128
Undrawn and other fees 654 424 341
Total interest expense $ 25,203 $ 16,347 $ 16,600