Fair Value Measurements - Additional Information (Details) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Jul. 31, 2018
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of financial liabilities measured at fair value on a recurring basis	$ 585,000	$ 585,000	$ 585,000
Changes in fair value of Level 3 liabilities	$ 0	$ 0
3.5% Convertible Notes Due 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument, interest rate, stated percentage	3.50%	3.50%		3.50%
Fair value of convertible debt	$ 112,000,000	$ 112,000,000	141,000,000
Carrying value of convertible debt	$ 152,634,000	$ 152,634,000	$ 148,101,000	$ 143,723,000

Amount of liability recognized arising from contingent consideration in a business combination.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
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Including the current and noncurrent portions, carrying amount of debt identified as being convertible into another form of financial instrument (typically the entity's common stock) as of the balance sheet date, which originally required full repayment more than twelve months after issuance or greater than the normal operating cycle of the company.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Fair value portion of borrowing which can be exchanged for a specified number of another security at the option of the issuer or the holder, for example, but not limited to, the entity's common stock.

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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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- Definition

Amount of gain (loss) recognized in income from liability measured at fair value on recurring basis using unobservable input (level 3).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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