Convertible Notes, Net - Summary of Details about Interest Expense (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Discount and issuance cost amortization			$ 20,993	$ 16,356
Convertible Senior Note [Member]
Debt Instrument [Line Items]
Cash coupon	$ 9,277	$ 6,247	25,333	12,732
Discount and issuance cost amortization	1,535	1,202	4,242	2,869
Total interest expense	$ 10,812	$ 7,449	$ 29,575	$ 15,601

Amount of amortization expense attributable to debt discount (premium) and debt issuance costs.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of the cost of borrowed funds accounted for as interest expense for debt.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Represents the portion of interest incurred in the period on debt arrangements that was charged against earnings, excluding amortization of debt discount (premium) and financing costs.

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