DEBT - Convertible Subordinated Notes (Details) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2013 USD ($) item $ / shares $ / item shares	Dec. 31, 2016 USD ($) $ / shares $ / item shares	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Debt
Proceeds from issuance of notes payable, net of debt issuance costs		$ 0	$ 0	$ 434,677
Settlement amount for purchase of notes		11,570	0	0
Amount received from capped call option		$ 578	$ 0	$ 0
Convertible subordinated notes due 2023
Debt
Loan amount	$ 287,500
Proceeds from issuance of notes payable, net of debt issuance costs	$ 281,200
Interest rate (as a percent)		2.125%
Initial conversion, shares per $1,000 principal amount | shares	35.9903
Adjusted conversion, shares per $1,000 principal amount | shares		50.5818
Conversion price of convertible notes into common stock (in dollars per share) | $ / shares	$ 27.79	$ 19.77
Portion of debt retired, face value		$ 14,100
Portion of debt retired, carrying value		13,900
Settlement amount for purchase of notes		11,600
Gain (Loss) on Repurchase of Debt Instrument		$ 2,300
Convertible subordinated notes due 2023 | Privately-negotiated capped call option
Debt
Payments for capped call options	$ 36,800
Number of derivative instruments purchased | item	2
Strike price for the underlying number of shares (in dollars per share) | $ / shares	$ 27.79	$ 19.77
Cap price for the underlying number of shares (in dollars per share) | $ / item	38.00	27.04
Amount received from capped call option		$ 600
Convertible subordinated notes due 2023 | Stock prices below $27.79 per share | Minimum
Debt
Net shares settlement payable to the entity | shares	0
Convertible subordinated notes due 2023 | Stock prices above $38.00 per share | Maximum
Debt
Net shares settlement payable to the entity | shares	2,779,659