Convertible 3.75% Senior Notes (Details) - Convertible Notes Payable - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Face amount of the Notes	$ 143,750,000	$ 143,750,000
Unamortized discount	18,178,000	20,517,000
Debt issuance costs	2,001,000	2,256,000
Carrying amount of the Notes	$ 123,571,000	$ 120,977,000

Including the current and noncurrent portions, carrying amount of debt identified as being convertible into another form of financial instrument (typically the entity's common stock) as of the balance sheet date, which originally required full repayment more than twelve months after issuance or greater than the normal operating cycle of the company.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 210
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