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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 835
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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- References

No definition available.

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Fair Value of Financial Instruments - Notes Payable (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Sep. 23, 2016	Jun. 30, 2015
Notes Payable \| 8.375% Notes due 2026
Fair value disclosures
Annual interest rate of notes (as a percent)	8.375%		8.375%
Aggregate principal amount of notes issued in private placement			$ 150,000
Notes Payable \| 8.375% Notes due 2026 \| Significant Unobservable Inputs (Level 3)
Fair value disclosures
Aggregate principal amount of notes issued in private placement			$ 150,000
Estimated fair value	$ 152,100	$ 152,500
Convertible Senior Notes \| 2.25% Convertible Senior Notes due in 2022
Fair value disclosures
Annual interest rate of notes (as a percent)	2.25%			2.25%
Aggregate principal amount of notes issued in private placement	$ 335,699	335,699		$ 335,700
Convertible Senior Notes \| 2.25% Convertible Senior Notes due in 2022 \| Significant Other Observable Inputs (Level 2)
Fair value disclosures
Estimated fair value	$ 445,600	$ 392,800