DEBT (Tables)

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Summary of Senior Subordinated Convertible Obligations

The Notes are senior subordinated convertible obligations, summarized as of December 31, as follows:

	2019		2018
1.50% senior subordinated convertible notes due in October 2020 (the 2020 Notes)	$	374,993	$	374,993
Unamortized discount	(12,078)		(26,581)
Unamortized deferred offering costs	(1,033)		(2,334)
Convertible Notes due 2020, net (1)	361,882		346,078
0.599% senior subordinated convertible notes due in August 2024 (the 2024 Notes)	495,000		495,000
Unamortized discount	(6,533)		(7,946)
Unamortized deferred offering costs	(2,229)		(2,715)
Convertible Notes due in 2024, net	486,238		484,339
Total convertible debt, net	$	848,120	$	830,417
Fair value of fixed rate convertible debt
Convertible Notes due in 2020 (2)	$	405,679	$	419,722
Convertible Notes due in 2024 (2)	521,839		491,626
Total	$	927,518	$	911,348

(1)As the 2020 Notes mature in October 2020, the outstanding principal of the 2020 Notes is classified as a current liability as of December 31, 2019.

(2)The fair value of the Company’s fixed-rate convertible debt is based on open market trades and is classified as Level 1 in the fair value hierarchy. See Note 3 to these Consolidated Financial Statements for additional information related to the Company’s fair value measurements.

Summary of Interest Expense on Debt

Interest expense on the Company’s debt consisted of the following:

	Years Ended December 31,
	2019		2018		2017
Coupon interest	$	4,907	$	12,452	$	10,407
Amortization of debt issuance costs	2,031		3,610		3,725
Accretion of discount on convertible notes	15,917		27,602		28,575
Total interest expense on convertible debt	$	22,855	$	43,664	$	42,707