Long-Term Debt - Schedule of Company's Long-Term Debt (Parenthetical) (Detail)	9 Months Ended	12 Months Ended
Sep. 30, 2017	Dec. 31, 2016
5.85% Convertible Senior Notes, due August 2037 [Member]
Debt Instrument [Line Items]
Maturity date	Aug. 01, 2037
Interest rate	5.85%
Senior Secured Note, due December 15, 2023 [Member]
Debt Instrument [Line Items]
Maturity date	Dec. 15, 2023	Dec. 15, 2023

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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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.

+ Details

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Balance Type:	na
Period Type:	duration

- Details

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Namespace Prefix:
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- Details

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