DEBT - Revolving Credit Facility (Details)				6 Months Ended
	Jul. 21, 2020 USD ($)	Dec. 10, 2019 USD ($)	Oct. 26, 2018 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Line of Credit Facility [Line Items]
Potential additional borrowing capacity		$ 185,000,000.0
Letters of credit outstanding				$ 200,000		$ 200,000
Ratio of Debt to EBITDA Step-Down		4.0
Ratio of Debt to EBITDA Increase		0.5
Unused commitment fees				1,300,000	$ 500,000
Amortization of debt issuance costs				2,547,000	1,158,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 500,000,000.0	$ 350,000,000.0
Debt term		5 years	5 years
Line of credit outstanding				0		$ 0
Collateral, percent of domestic subsidiaries equity		100.00%
Collateral, percent of voting equity		66.00%
Collateral, percent of non-voting equity		100.00%
Collateral, percent of assets		100.00%
Collateral, percent of equity		100.00%
Letter of credit fronting fee percentage		0.125%
Fees and expense paid to lenders at closing	$ 1,100,000		$ 2,800,000
Swingline Facility
Line of Credit Facility [Line Items]
Covenant amount		$ 10,000,000.0
Letters of Credit
Line of Credit Facility [Line Items]
Covenant amount		$ 10,000,000.0
Fed Funds Effective Rate | Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate		0.50%
LIBOR | Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate		1.00%
Interest expense					1,100,000
Minimum | Revolving Credit Facility
Line of Credit Facility [Line Items]
Unused capacity, commitment fee percentage		0.25%
Letter of credit participation fee percentage		1.25%
Minimum | LIBOR | Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate		1.25%
Minimum | Base Rate | Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate		0.25%
Maximum
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 | Revolving Credit Facility
Line of Credit Facility [Line Items]
Unused capacity, commitment fee percentage		0.45%
Letter of credit participation fee percentage		2.00%
Maximum | LIBOR | Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate		2.00%
Maximum | Base Rate | Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate		1.00%
Revolving Credit Facility
Line of Credit Facility [Line Items]
Interest expense				2,300,000	2,100,000
Amortization of debt issuance costs				$ 1,000,000.0	$ 500,000
Line of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Covenant amount	$ 200,000,000.0
Floor interest rate	0.75%
Unused capacity, commitment fee percentage	0.50%
Line of Credit | LIBOR | Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.25%
Line of Credit | Base Rate | Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.25%