Notes Payable - 2.25% Convertible Senior Notes due 2022 - Total Interest Expense (Details) - 2.25% Convertible Senior Notes due in 2022 - Convertible Senior Notes - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Interest Expense
Contractual interest expense	$ 1,888	$ 1,888
Amortization of debt issuance costs	187	153
Amortization of debt discount	3,421	3,135
Total interest expense	$ 5,496	$ 5,176

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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Amount of amortization expense attributable to debt issuance costs.

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Amount of the cost of borrowed funds accounted for as interest expense for debt.

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