Debt Instrument, Conversion Premium

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- Definition

Debt Instrument, Convertible, Conversion Rate

+ References

No definition available.

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- Definition

Debt Instrument, Covenant, Change in Control, Redemption Price, Percentage

+ References

No definition available.

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- Definition

Debt Instrument, Covenant, Collateral Coverage Ratio, Calculation, Amount Added to Cash and Cash Equivalents

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No definition available.

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- Definition

Debt Instrument, Covenant, Collateral Coverage Ratio Calculation, Average Grantor EBITDA Multiplier for Seven Most Recent Fiscal Quarters

+ References

No definition available.

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- Definition

Debt Instrument, Covenant, Collateral Coverage Ratio, Minimum

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Covenant, Minimum Fixed Charge Coverage Ratio, Available Borrowings Threshold

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Covenant, Minimum Fixed Charge Coverage Ratio, Available Borrowings Threshold, Percent of Lender Commitments

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Covenant, Required Collateral Coverage Ratio Not Met, Redemption Period

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Covenant, Required Collateral Coverage Ratio Not Met, Redemption Price, Percentage

+ References

No definition available.

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- Definition

Debt Instrument, Debt Default, Triggering Event Threshold, Amount

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Redemption, Percentage of Notes

+ References

No definition available.

+ Details

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- Definition

Line of Credit Facility, Accordion Feature, Increase Limit

+ References

No definition available.

+ Details

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- Definition

Line of Credit Facility, Springing Maturity Date, Period Prior to Maturity Date of Convertible Debt

+ References

No definition available.

+ Details

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- Definition

Line of Credit Facility, Springing Maturity Date, Period Prior to Maturity Date of Secured Debt

+ References

No definition available.

+ Details

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- Definition

Payments for Capped Call Transactions

+ References

No definition available.

+ Details

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
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- Definition

The number of equity instruments that the holder of the debt instrument would receive if the debt was converted to equity.

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- Definition

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

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+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
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- Definition

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

+ References

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- Definition

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.

+ References

No definition available.

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- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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- Definition

Percentage of principal amount of debt redeemed.

+ References

No definition available.

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

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Debt - Additional Information (Detail)	9 Months Ended	12 Months Ended
Debt - Additional Information (Detail)	Sep. 30, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) shares $ / shares	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)
Senior Secured Notes Due 2022 \| Senior Notes
Debt Instrument [Line Items]
Aggregate principal amount		$ 440,000,000
Interest rate		10.75%
Redemption price, percent of principal amount of notes redeemed		100.00%
Percent of notes with option to redeem		35.00%
Redemption price, percentage of principal amount		110.75%
Redemption price if required collateral coverage ratio not met, percentage of principal amount		100.00%
Minimum collateral coverage ratio		1.5
Collateral coverage ratio, amount added to cash and cash equivalents		4.75
Collateral coverage ratio, multiplier for Average Grantor EBITDA for seven most recent fiscal quarters		4
Period to redeem notes without default if required collateral coverage ratio not met		90 days
Redemption price if company experiences change of control, percent of principal amount		101.00%
5.50% convertible senior notes due 2021
Debt Instrument [Line Items]
Aggregate principal amount			$ 1,000
5.50% convertible senior notes due 2021 \| Senior Notes
Debt Instrument [Line Items]
Aggregate principal amount	$ 213,500,000	$ 213,500,000	$ 213,500,000
Interest rate	5.50%		5.50%
Effective interest rate			9.50%
Debt conversion rate (in shares) \| shares			102.4249
Total number of convertible shares (in shares) \| shares			21,867,716
Conversion price (in dollars per share) \| $ / shares	$ 12.75		$ 9.76
Payments for capped call transactions			$ 27,300,000
Conversion premium percentage	60.00%		22.50%
Credit Agreement \| Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 145,000,000	$ 125,000,000.0
Accordion feature increase limit	$ 150,000,000
Borrowings outstanding	0
Available borrowings	$ 103,400,000
Springing maturity date, period prior to maturity date of convertible debt	91 days
Springing maturity date, period prior to maturity date of secured debt	60 days
Credit Agreement \| Letter of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 30,000,000
Letters of credit outstanding	$ 6,400,000
Credit Agreement \| Line of Credit \| Revolving Credit Facility
Debt Instrument [Line Items]
Requirement to maintain minimum fixed charge coverage ratio, availability threshold, percent of lenders' commitments under facility	10.00%
Requirement to maintain minimum fixed charge coverage ratio, availability threshold	$ 15,000,000
Amount of aggregate default under other debt that would trigger event of default	$ 50,000,000