INCOME TAXES - Effective tax rate - (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019
Effective income tax rate differs from the statutory rate
U.S. statutory rate (as a percent)	21.00%	21.00%	21.00%
State income taxes, net (as a percent)	2.10%	2.20%	2.20%
Exempt municipal bond interest (as a percent)		(0.10%)	(0.10%)
Foreign tax rates (as a percent)	1.00%	(0.10%)	0.50%
Income tax credits and adjustments (as a percent)	(1.40%)	0.50%
Adjustment of deferred tax balances (as a percent)	(0.20%)		0.10%
Reserve for uncertain tax benefits (as a percent)	(0.80%)	0.40%	(1.00%)
Other, net (as a percent)	1.00%	0.20%	(0.30%)
Effective income tax rate (as a percent)	22.70%	24.10%	22.40%
Unrecognized tax benefits	$ 3,678	$ 3,339	$ 3,339	$ 3,011	$ 3,678
Portion of unrecognized tax benefits that, if recognized, would favorably affect annual effective income tax rate				1,468	2,012
Interest and penalties included in liability for uncertain tax positions				340	$ 562
Reconciliation of the beginning and ending balances of the total amounts of unrecognized tax benefits
Unrecognized tax benefits at the beginning of the period	3,678	3,339	4,342
Increases in tax positions for the current year	377	1,164	448
Reductions in tax positions for lapse of statute of limitations	(501)	(576)	(751)
Reductions in tax positions for settlements and payments	(308)	(249)
Decreases in prior period unrecognized tax benefits	(235)		(700)
Unrecognized tax benefits at the end of the period	$ 3,011	$ 3,678	$ 3,339
Spain
Effective income tax rate differs from the statutory rate
Tax benefits of foreign subsidiary tax loss carry forwards expiring in 2026				306
Tax benefits of foreign subsidiary tax loss carry forwards expiring in 2027				65
Tax benefits of foreign subsidiary tax loss carry forwards expiring in 2028				194
Tax benefits of foreign subsidiary tax loss carry forwards expiring in 2029				111
Tax benefits of foreign subsidiary tax loss carry forwards expiring in 2030				335
Tax benefits of foreign subsidiary tax loss carry forwards expiring in 2031				447
Tax benefits of foreign subsidiary tax loss carry forwards expiring in 2032				337
Tax benefits of foreign subsidiary tax loss carry forwards expiring in 2033				136
Tax benefits of foreign subsidiary tax loss carry forwards expiring in 2034				470
Tax benefits of foreign subsidiary tax loss carry forwards expiring in 2035				594
Tax benefits of foreign subsidiary tax loss carry forwards expiring in 2036				863
Tax benefits of foreign subsidiary tax loss carry forwards expiring in 2037				440
Tax benefits of foreign subsidiary tax loss carry forwards expiring in 2038				$ 210