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Amount of amortization expense attributable to debt issuance costs.

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Including the current and noncurrent portions, the carrying value of convertible subordinated debt, as of the balance sheet date, initially scheduled to be repaid after one year or beyond the normal operating cycle if longer. This form of debt can be exchanged for a specified amount of another security, typically the entity's common stock, at the option of the issuer or the holder, and places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

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The carrying amount of the equity component of convertible debt which may be settled in cash upon conversion.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount, after accumulated amortization, of debt discount.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of convertible debt securities using the if-converted method.

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

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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Amount of accretion of discount for the standardized measure of discounted future net cash flow related to proved oil and gas reserves.

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Convertible Subordinated Notes (Details) - USD ($) shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Sep. 30, 2016	Mar. 19, 2014
Debt Instrument [Line Items]
Effect of dilutive securities, Convertible junior subordinated debentures (in shares)	1,230	1,090
Carrying Values of Liability and Equity Components, Convertible Subordinated Notes
Debt issuance costs	$ (891,000)		$ (967,000)
Accumulated Amortization, Debt Issuance Costs	4,518,000		4,442,000
Amortization of Debt Issuance Costs	208,000	$ 203,000
Convertible Subordinated Notes [Member]
Debt Instrument [Line Items]
Stated interest rate percentage					2.75%
Carrying Values of Liability and Equity Components, Convertible Subordinated Notes
Convertible subordinated notes, principal amount	143,750,000		143,750,000		$ 143,750,000
Unamortized discount of liability component	(16,398,000)		(17,559,000)
Debt issuance costs	(1,619,000)		(1,750,000)
Accumulated Amortization, Debt Issuance Costs	1,746,000		1,359,000
Carrying value of the liability component	125,733,000		124,441,000
Equity component carrying value	17,973,000		$ 17,973,000
Convertible subordinated notes, fair value	188,600,000
Contractual coupon interest expense	1,000,000	1,000,000
Accretion of discount, convertible subordinated notes	$ 1,200,000	1,000,000
Effective interest rate percentage	2.75%			6.75%
Amortization of Debt Issuance Costs	$ 100,000	$ 100,000