CONVERTIBLE DEBT (Tables)

12 Months Ended

Dec. 31, 2015

Summary of Additional Noncash Interest Expense Recognized During the Period

The following table summarizes the additional interest expense recognized for the accretion of the debt discount and amortization of the deferred offering costs.

	Years Ended December 31,
	2015		2014		2013
Convertible Notes due 2018
Amortization of issuance costs	$	1,921	$	1,910	$	397
Accretion of debt discount		13,633		12,963		2,620
Convertible Notes due 2020
Amortization of issuance costs		1,283		1,279		264
Accretion of debt discount		11,567		10,930		2,201
Total	$	28,404	$	27,082	$	5,482

Summary of Convertible Debt

The following table summarizes information regarding the Company’s convertible debt at December 31:

	2015					2014
Convertible Notes due 2020	$	374,993				$	375,000
Unamortized discount		(65,478	)				(77,045	)
Unamortized deferred offering costs		(6,210	)				(7,493	)
Convertible Notes due 2020, net					303,305					290,462
Convertible Notes due 2018		374,980					375,000
Unamortized discount		(41,904	)				(55,537	)
Unamortized deferred offering costs		(5,415	)				(7,335	)
Convertible Notes due 2018, net					327,661					312,128
Convertible Notes due 2017		31,430					40,558
Unamortized deferred offering costs		(110	)				(246	)
Convertible Notes due 2017, net					31,320					40,312
Total convertible debt, net				$	662,286				$	642,902
Fair value of fixed rate convertible debt
Convertible Notes due in 2020 ⁽¹⁾				$	502,701				$	456,360
Convertible Notes due in 2018 ⁽¹⁾					482,584					442,448
Convertible Notes due in 2017 ⁽¹⁾					162,016					180,984
Total				$	1,147,301				$	1,079,792

(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 Convertible Debt Interest Expense

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

	Years Ended December 31,
	2015		2014		2013
Coupon interest	$	9,750	$	9,417	$	4,550
Amortization of issuance costs		3,294		3,332		1,053
Accretion of debt discount		25,200		23,893		4,821
Total interest expense on convertible debt	$	38,244	$	36,642	$	10,424