DEBT (Tables)

6 Months Ended

Jun. 30, 2017

Debt Disclosure [Abstract]

Summary of Convertible Debt

Convertible Notes

The following table summarizes information regarding the Company’s convertible debt:

	June 30,			December 31,
	2017			2016
Convertible Notes due in 2017	$	—		$	22,503
Unamortized deferred offering costs		—			(25	)
Convertible Notes due in 2017, net		—			22,478
Convertible Notes due in 2018		374,980			374,980
Unamortized discount		(20,122	)		(27,566	)
Unamortized deferred offering costs		(2,515	)		(3,484	)
Convertible Notes due in 2018, net		352,343			343,930
Convertible Notes due in 2020		374,993			374,993
Unamortized discount		(46,854	)		(53,239	)
Unamortized deferred offering costs		(4,277	)		(4,923	)
Convertible Notes due in 2020, net		323,862			316,831
Total convertible debt, net	$	676,205		$	683,239
Fair value of fixed rate convertible debt
Convertible Notes due in 2017 (1)	$	—		$	90,977
Convertible Notes due in 2018 (1)		416,337			423,202
Convertible Notes due in 2020 (1)		446,725			442,754
Total	$	863,062		$	956,933

(1) 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.

Summary of Interest Expense on Debt

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2017		2016		2017		2016
Coupon interest	$	2,194	$	2,520	$	4,558	$	5,026
Amortization of issuance costs		886		825		1,772		1,649
Accretion of debt discount		6,960		6,599		13,829		13,112
Total interest expense on convertible debt	$	10,040	$	9,944	$	20,159	$	19,787