The period in days that the note holder may convert all or a portion of the convertible note.

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Minimum percentage of the product of the last reported note sale price and the conversion rate to determine eligibility of 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. The calculation does not take the note holder's put option into consideration.

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Amount of accrued and unpaid interest.

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Represents the outstanding principal amount plus interest accrued and unpaid.

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Aggregate dividends paid during the period for each share of common stock outstanding.

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Year of expiration or mandatory redemption of the financial instrument issued in exchange for the original debt being converted in a noncash or part noncash transaction, in CCYY format.

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The price per share of the conversion feature embedded in the debt instrument.

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Ratio applied to the conversion of debt instrument into equity with equity shares divided by debt principal amount.

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Remaining amortization period for discount on the liability component of convertible debt which may be settled in cash upon conversion, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Description of the conversion terms of a debt instrument which may include the conversion ratio (including all potential conversion ratios if contingently adjustable), type of debt or equity security into which the debt is convertible, the dollars of debt or the number of shares into which the instrument is convertible (or potentially convertible into), the conversion period, any contingencies associated with the conversion terms, and the existence and amount of a beneficial conversion feature.

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Threshold period of specified consecutive trading days within which common stock price to conversion price of convertible debt instrument must exceed threshold percentage for specified number of trading days to trigger conversion feature.

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Minimum percentage of common stock price to conversion price of convertible debt instruments to determine eligibility of conversion.

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Threshold number of specified trading days that common stock price to conversion price of convertible debt instruments must exceed threshold percentage within a specified consecutive trading period to trigger conversion feature.

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- Definition

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

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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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Date the debt instrument was repurchased, in CCYY-MM-DD format.

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Face (par) amount of the original debt instrument that was repurchased.

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No definition available.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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No definition available.

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

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate.

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The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

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No definition available.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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Long-Term Debt (Convertible Senior Notes) - Additional Information (Detail) $ / shares in Units, $ in Thousands			1 Months Ended	3 Months Ended	9 Months Ended
	Apr. 03, 2017 USD ($)	Mar. 03, 2017 USD ($)	Jan. 31, 2015 $ / shares	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2017 USD ($) d $ / shares	Dec. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2013 USD ($)
Debt Instrument [Line Items]
Debt instrument, face amount				$ 260,317	$ 260,317	$ 147,985
Debt extinguishment costs					$ (743)
3.875% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate				3.875%	3.875%
Debt conversion date					2019
Debt instrument, face amount				$ 89,990	$ 89,990	89,990	$ 89,990	$ 103,000
Aggregate amount of debt repurchased							$ 13,010
Convertible debt, conversion ratio				16.1801	16.1801
Convertible debt, conversion price \| $ / shares				$ 61.80	$ 61.80
Debt instrument, effective interest rate				8.30%	8.30%
Debt discount, remaining amortization period					1 year 6 months
3.875% Convertible Senior Notes [Member] \| Convertible Debt Instrument Conversion Period Two [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Cash dividends on common stock \| $ / shares			$ 0.275
4.25% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate	4.25%	4.25%		4.25%	4.25%
Debt conversion date					2037
Debt instrument, face amount		$ 143,750		$ 143,750	$ 143,750
Proceeds from senior convertible notes net		138,775
Debt issuance and transaction costs		$ 4,975
Convertible debt, conversion ratio				16.2635	16.2635
Convertible debt, conversion price \| $ / shares				$ 61.49	$ 61.49
Debt instrument, effective interest rate				7.60%	7.60%
Debt discount, remaining amortization period					4 years 4 months 24 days
Debt Instrument effective Rate					5.40%
Debt Instrument term					20 years
4.25% Convertible Senior Notes [Member] \| Debt Instrument, Redemption, Period One [Member]
Debt Instrument [Line Items]
Repurchase date of convertible notes					Mar. 01, 2022
4.25% Convertible Senior Notes [Member] \| Debt Instrument, Redemption, Period Two [Member]
Debt Instrument [Line Items]
Repurchase date of convertible notes					Mar. 01, 2027
4.25% Convertible Senior Notes [Member] \| Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Repurchase date of convertible notes					Mar. 01, 2032
Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				$ 233,740	$ 233,740	89,990
Convertible debt, conversion debt description					The note holders of the Convertible Senior Notes may convert all or a portion of their Convertible Senior Notes during specified periods as follows: (1) during any calendar quarter commencing after the calendar quarter ending on the dates specified in each respective indenture, if the last reported sale price of the Company’s common stock for at least 20 trading days during the period of 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter is greater than 130% of the conversion price on each applicable trading day; (2) during the five business-day period after any ten consecutive trading-day period in which the trading price per $1 principal amount of the Convertible Senior Notes is less than 98% of the product of the last reported sale price and the conversion rate on each such trading day; (3) if specified corporate events, including a change in control, occur; or (4) at any time on or after the dates specified in each respective indenture.
Convertible debt, threshold trading days \| d					20
Convertible debt, threshold consecutive trading days \| d					30
Convertible debt, threshold percentage of stock trigger price					130.00%
Convertible Senior Notes [Member] \| Convertible Debt Instrument Conversion Period Two [Member]
Debt Instrument [Line Items]
Convertible debt, threshold consecutive trading days \| d					10
Convertible debt, threshold trading days					5 days
Convertible debt, threshold percentage of stock trigger price					98.00%
Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, face amount						$ 40,250
Extinguishment of debt	$ 40,805
Fixed annual rate of interest	8.00%			8.00%	8.00%
Unamortized debt issuance costs	$ 743
Accrued and unpaid interest	$ 555
Debt extinguishment costs					$ 743