Summary of Other Income and Loss (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Nonoperating Income Expense [Abstract]
Interest expense	$ (10,681)	$ (802)	$ (26,460)	$ (1,325)
Interest income	1,477	438	5,236	813
Amortization of investment discount	2,295	433	5,123	693
Other (expense) income	(59)	115	(570)	522
Gain from sale of Priority Review Voucher				125,000
Other (loss) income	$ (6,968)	$ 184	$ (16,671)	$ 125,703

The sum of the periodic adjustments of the differences between securities' face values and purchase prices that are charged against earnings. This is called accretion if the security was purchased at a discount and amortization if it was purchased at premium. As a noncash item, this element is an adjustment to net income when calculating cash provided by or used in operations using the indirect method.

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Amount of gain (loss) on sale or disposal of intangible assets.

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Amount of the cost of borrowed funds accounted for as interest expense.

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Amount before accretion (amortization) of purchase discount (premium) of interest income on nonoperating securities.

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The aggregate amount of income or expense from ancillary business-related activities (that is to say, excluding major activities considered part of the normal operations of the business).

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Amount of income (expense) related to nonoperating activities, classified as other.

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