NET INCOME (LOSS) PER SHARE - Schedule of Earnings (Loss) Per Share and Dilutive Shares Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Basic net income (loss) per share
Net income (loss)	$ 3,331	$ (13,605)	$ (14,301)	$ 48,270	$ (21,048)	$ 33,824	$ (24,575)	$ 61,046
Denominator for basic net income (loss) per share (in shares)	72,747			63,917			67,332	63,714
Add: Interest expense on convertible debt, net of tax	$ 0			$ 5,340			$ 0	$ 15,815
Basic net (loss) income per share (in dollars per share)	$ 0.05			$ 0.76			$ (0.36)	$ 0.96
Add effect of diluted securities:
Stock options and equivalents and convertible debt (in shares)	0			18,773			0	18,568
Denominator for diluted net income (loss) per share (in shares)	72,747			82,690			67,332	82,282
Diluted net income (loss) per share (in dollars per share)	$ 0.05			$ 0.65			$ (0.36)	$ 0.93
Potentially dilutive common shares:
Total potentially dilutive common shares (in shares)	39,293			2,741			29,484	3,359
Convertible debt | 2.50% Convertible Notes due 2021
Potentially dilutive common shares:
Total potentially dilutive common shares (in shares)	12,313			0			16,038	0
Convertible debt | 5.00% Convertible Notes due 2024
Potentially dilutive common shares:
Total potentially dilutive common shares (in shares)	20,262			0			6,828	0
Stock options and equivalents
Potentially dilutive common shares:
Total potentially dilutive common shares (in shares)	6,718			2,741			6,618	3,359