Convertible Debentures and Credit Arrangements - Convertible Senior Debentures Narrative (Detail) - Convertible Senior Debentures due 2018 - USD ($)	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Nov. 30, 2012
Debt Instrument [Line Items]
Aggregate face value of convertible senior debentures	$ 55,000,000		$ 55,000,000.0
Interest rate on debentures			5.25%
Fair value of debentures outstanding	56,100,000
Gross carrying amount of equity component	6,400,000
Unamortized discount	1,600,000
Deferred finance costs, noncurrent, net	400,000
Carrying value of liability component	53,000,000
Amortization of debt discount (premium)	$ 400,000	$ 300,000
Debt instrument, interest rate, effective percentage	8.70%

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

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Face (par) amount of debt instrument at time of issuance.

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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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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Amount, after accumulated amortization, of debt discount.

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

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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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