DEBT (Senior Secured Revolving Credit Facility) (Details) $ in Thousands			3 Months Ended	12 Months Ended
	Dec. 10, 2019 USD ($)	Nov. 21, 2017	Dec. 31, 2017 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) Rate	Dec. 31, 2017 USD ($)	Oct. 31, 2018 USD ($)	Oct. 26, 2018 USD ($)
Line of Credit Facility [Line Items]
Revolving credit facility, outstanding amount				$ 75,000	$ 125,000
Interest rate				3.01%	4.02%
Credit Agreement, potential additional borrowing capacity	$ 185,000
Credit Agreement, ratio of debt to EBITDA	2.50
Letters of credit outstanding				$ 200
Ratio of debt to EBITDA step-down		4.0
Ratio of debt to EBITDA Increase		0.5
Write-off of previously-capitalized debt issuance costs				333	$ 0	$ 90
Interest expense				15,300	14,600	8,200
Amortization of debt issuance costs				1,974	1,776	1,032
Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 500,000							$ 350,000
Revolving credit facility, term	5 years
Percent of domestic subsidiaries equity		100.00%
Percent of voting equity		66.00%
Percent of non-voting equity		100.00%
Revolving credit facility, collateral, percent of assets		100.00%
Revolving credit facility, collateral, percent of equity		100.00%
Revolving credit facility, letter of credit fronting fee percentage		0.125%
Write-off of previously-capitalized debt issuance costs			$ 100	300
Revolving credit facility, debt issuance costs							$ 2,800
Interest expense				6,100	2,000
Unused borrowing capacity fee				600	800	500
Amortization of debt issuance costs				600	400	$ 400
Swingline Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 10,000
Letter of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 10,000
Fed Funds Effective Rate Overnight Index Swap Rate | Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit facility, basis spread on variable rate	0.50%
LIBOR | Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit facility, basis spread on variable rate	1.00%
Interest expense				4,900	$ 800
Minimum | Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit facility, unused capacity, commitment fee percentage		0.25%
Revolving credit facility, letter of credit participation fee percentage		1.25%
Minimum | ABR | Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit facility, basis spread on variable rate	0.25%
Minimum | LIBOR | Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit facility, basis spread on variable rate	1.25%
Maximum
Line of Credit Facility [Line Items]
Ratio of debt to EBITDA		4.5
Maximum | Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit facility, unused capacity, commitment fee percentage		0.45%
Revolving credit facility, letter of credit participation fee percentage		2.00%
Maximum | ABR | Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit facility, basis spread on variable rate	1.00%
Maximum | LIBOR | Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit facility, basis spread on variable rate	2.00%
31 Day Borrowing, first | Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit facility, outstanding amount				50,000
31 Day Borrowing, second | Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit facility, outstanding amount				$ 25,000