DEBT - Narrative (Details)		1 Months Ended	9 Months Ended	12 Months Ended
	Sep. 17, 2019 USD ($)	Jan. 31, 2018 USD ($) shares	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) shares day $ / shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jun. 05, 2018 USD ($)	Apr. 28, 2015 USD ($)
Line of Credit Facility [Line Items]
Proceeds from convertible notes offering				$ 0	$ 172,500,000	$ 0
Total long-term debt				705,000,000	661,082,000
Long-term Debt, Fiscal Year Maturity [Abstract]
2020				5,000,000
2021				7,500,000
2022				10,000,000
2023				182,500,000
2024				200,000,000
Thereafter				300,000,000
Total				705,000,000
Letters of credit outstanding				3,900,000
Interest paid				$ 22,100,000	18,400,000	$ 8,600,000
7.50% Senior Notes Due 2027
Line of Credit Facility [Line Items]
Debt instrument, redemption price, percentage	100.00%
Convertible Senior Notes Due 2023
Long-term Debt, Fiscal Year Maturity [Abstract]
Number of equity instruments | shares		1,962,790
Revolving Credit Facility
Line of Credit Facility [Line Items]
Commitment fee rate				0.20%
Weighted average interest rate				4.59%
Revolving Credit Facility | The Lenders | 2015 Credit Facility
Line of Credit Facility [Line Items]
Convertible debt face amount								$ 417,300,000
Senior Notes | 7.50% Senior Notes Due 2027
Line of Credit Facility [Line Items]
Convertible debt face amount	$ 300,000,000
Convertible debt stated interest rate	7.50%
Effective rate	7.83%
Debt issuance costs, gross	$ 6,000,000.0			$ 5,844,000	0
Debt instrument, redemption price, percentage	107.50%
Debt redemption, change of control	101.00%
Term Loan
Line of Credit Facility [Line Items]
Total long-term debt				$ 97,500,000	96,250,000
Weighted average interest rate				4.53%
Term Loan | 2019 Credit Facility
Line of Credit Facility [Line Items]
Convertible debt face amount	$ 100,000,000
Increase (decrease) in borrowing capacity	250,000,000
Term Loan | 2018 Credit Facility
Line of Credit Facility [Line Items]
Convertible debt face amount							$ 100,000,000
Gain (loss) on extinguishment of debt	(700,000)
Term Loan | Revolving Credit Facility | The Lenders
Line of Credit Facility [Line Items]
Maximum borrowing capacity								$ 82,700,000
Line of Credit
Line of Credit Facility [Line Items]
Total long-term debt				$ 135,000,000	392,332,000
Line of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Ratio of indebtedness to net capital				4.50
Line of Credit | Revolving Credit Facility | 2019 Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 550,000,000
Ratio of indebtedness to net capital				4.00
Consolidated fixed charge coverage ratio, actual				150.00%
Line of Credit | Revolving Credit Facility | 2018 Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity							$ 800,000,000
Convertible Debt
Line of Credit Facility [Line Items]
Total long-term debt				$ 172,500,000	$ 172,500,000
Convertible Debt | Convertible Senior Notes Due 2023
Line of Credit Facility [Line Items]
Convertible debt face amount		$ 172,500,000
Convertible debt stated interest rate		1.00%
Effective rate				5.25%	5.25%
Proceeds from convertible notes offering				$ 167,500,000
Debt issuance costs, gross		$ 4,100,000
Variable rate				1.00%
Long-term Debt, Fiscal Year Maturity [Abstract]
Unamortized discount		$ 36,000,000.0
Unamortized debt discount, difference In aggregate face amount and future cash flows				$ 31,900,000
Convertible debt conversion ratio				11.3785
Number of equity instruments | shares				1,962,790
Convertible debt conversion price (in dollars per share) | $ / shares				$ 87.89
London Interbank Offered Rate (LIBOR) | Revolving Credit Facility
Line of Credit Facility [Line Items]
Effective rate				3.31%
Variable rate				1.50%
Long-term line of credit				$ 135,000,000.0
London Interbank Offered Rate (LIBOR) | Revolving Credit Facility | 2018 Credit Facility
Line of Credit Facility [Line Items]
Variable rate					4.56%
London Interbank Offered Rate (LIBOR) | Term Loan
Line of Credit Facility [Line Items]
Total long-term debt				$ 97,500,000
London Interbank Offered Rate (LIBOR) | Term Loan | Revolving Credit Facility | 2018 Credit Facility
Line of Credit Facility [Line Items]
Total long-term debt					$ 96,300,000
London Interbank Offered Rate (LIBOR) | Term Loan | Revolving Credit Facility | The Lenders | 2018 Credit Facility
Line of Credit Facility [Line Items]
Long-term line of credit					$ 388,000,000.0
Prime Rate | Revolving Credit Facility | The Lenders | 2018 Credit Facility
Line of Credit Facility [Line Items]
Variable rate					1.00%
Base Rate | Revolving Credit Facility | 2018 Credit Facility
Line of Credit Facility [Line Items]
Variable rate					6.50%
Weighted average interest rate					4.20%
Base Rate | Revolving Credit Facility | The Lenders | 2018 Credit Facility
Line of Credit Facility [Line Items]
Variable rate					2.00%
Long-term line of credit					$ 4,300,000
Base Rate | Term Loan | Revolving Credit Facility | 2018 Credit Facility
Line of Credit Facility [Line Items]
Weighted average interest rate					4.05%
September 30, 2019 through June 30, 2021 | Term Loan | 2019 Credit Facility
Line of Credit Facility [Line Items]
Required periodic payment			$ 1,250,000
September 30, 2021 and thereafter | Term Loan | 2019 Credit Facility
Line of Credit Facility [Line Items]
Required periodic payment			$ 2,500,000
Redemption eriod one | Convertible Debt | Convertible Senior Notes Due 2023
Long-term Debt, Fiscal Year Maturity [Abstract]
Threshold of consecutive trading days				30
Threshold percentage of stock price trigger				130.00%
Redemption period two | Convertible Debt | Convertible Senior Notes Due 2023
Long-term Debt, Fiscal Year Maturity [Abstract]
Threshold of consecutive trading days | day				5
Threshold percentage of stock price trigger				98.00%
Threshold of trading days | day				5
Maximum
Line of Credit Facility [Line Items]
Debt Instrument, unused borrowing capacity, fee				$ 0.00225
Maximum | Senior Notes | 7.50% Senior Notes Due 2027
Line of Credit Facility [Line Items]
Debt instrument, redemption price, percentage	40.00%
Maximum | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Variable rate				1.75%
Maximum | Prime Rate
Line of Credit Facility [Line Items]
Variable rate				0.75%
Minimum
Line of Credit Facility [Line Items]
Debt Instrument, unused borrowing capacity, fee				$ 0.0015
Minimum | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Variable rate				1.00%
Minimum | Prime Rate
Line of Credit Facility [Line Items]
Variable rate				0.00%
Minimum | Redemption eriod one | Convertible Debt | Convertible Senior Notes Due 2023
Long-term Debt, Fiscal Year Maturity [Abstract]
Threshold of consecutive trading days				20