REVOLVING CREDIT FACILITY (Details) - USD ($)		3 Months Ended	12 Months Ended
	Nov. 21, 2017	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 31, 2018
Line of Credit Facility [Line Items]
Revolving credit facility, outstanding amount		$ 0	$ 125,000,000	$ 0
Long-term Debt, Weighted Average Interest Rate, at Point in Time			4.02%
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			$ 0	90,000	$ 0
Interest Expense, Debt			14,600,000	8,200,000
Debt Instrument, Unused Borrowing Capacity, Fee			800,000	500,000
Amortization of debt issuance costs			1,776,000	1,032,000	$ 245,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Revolving credit facility, current borrowing capacity	$ 250,000,000					$ 350,000,000.0
Revolving credit facility, term	5 years
Revolving credit facility, conditional increase to borrowing capacity	$ 100,000,000.0
Line Of Credit Facility, Increase Limit						100,000,000.0
Line of Credit Facility, Collateral, Percent of Domestic Subsidiaries Equity	100.00%
Line of Credit Facility, Collateral, Percent of Voting Equity	66.00%
Line of Credit Facility, Collateral, 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		$ 100,000
Revolving credit facility, debt issuance costs						$ 500,000
Swingline Facility [Member]
Line of Credit Facility [Line Items]
Revolving credit facility, current borrowing capacity	$ 10,000,000.0
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Revolving credit facility, current borrowing capacity	$ 10,000,000.0
Federal Funds Effective Swap Rate [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Revolving credit facility, basis spread on variable rate	0.50%
London Interbank Offered Rate (LIBOR) [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Revolving credit facility, basis spread on variable rate	1.00%
Minimum [Member] | Revolving Credit Facility [Member]
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 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Revolving credit facility, basis spread on variable rate	1.25%
Minimum [Member] | Base Rate [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Revolving credit facility, basis spread on variable rate	0.25%
Maximum [Member]
Line of Credit Facility [Line Items]
Ratio of Debt to EBITDA to Increase Revolving Commitment	2.50
Ratio of Debt to EBITDA	4.5
Maximum [Member] | Revolving Credit Facility [Member]
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 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Revolving credit facility, basis spread on variable rate	2.00%
Maximum [Member] | Base Rate [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Revolving credit facility, basis spread on variable rate	1.00%
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Interest Expense, Debt			2,000,000
Amortization of debt issuance costs			400,000	$ 400,000
Revolving Credit Facility, Borrowings At Base Rate Plus LIBOR [Member]
Line of Credit Facility [Line Items]
Interest Expense, Debt			$ 800,000