Interest Expense on Convertible Senior Notes (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Debt Instrument
Contractual interest expense on the coupon	$ 5,750	$ 5,750
Amortization of the discount component and debt issue fees recognized as interest expense	14,706	13,995
Total interest expense on the convertible debt	$ 20,456	$ 19,745

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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