SEGMENT INFORMATION - Segment Information Applicable to Reportable Operating Segments (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information
Number of reportable segments | segment			3
Number of operating segments | segment			3
Net sales:
Net sales	$ 652,752	$ 729,410	$ 1,914,603	$ 2,103,407
Operating income (loss):
Operating income (loss)	21,077	32,637	52,315	82,369
Interest (expense) income, net	(17)	62	80	444
Income before taxes	21,060	32,699	52,395	82,813
Depreciation and amortization:
Depreciation and amortization	3,833	3,107	10,335	10,184
Total assets:
Total assets	1,003,334	870,648	1,003,334	870,648	$ 937,335
Goodwill	73,602		73,602		$ 73,602
Business Solutions
Net sales:
Net sales	230,985	273,756	700,859	797,740
Enterprise Solutions
Net sales:
Net sales	259,767	278,295	839,943	871,969
Public Sector Solutions
Net sales:
Net sales	162,000	177,359	373,801	433,698
Operating Segments | Business Solutions
Net sales:
Net sales	230,985	273,756	700,859	797,740
Operating income (loss):
Operating income (loss)	8,827	13,533	21,579	38,509
Depreciation and amortization:
Depreciation and amortization	159	149	477	447
Total assets:
Total assets	343,010	300,360	343,010	300,360
Operating Segments | Enterprise Solutions
Net sales:
Net sales	259,767	278,295	839,943	871,969
Operating income (loss):
Operating income (loss)	14,843	16,346	45,233	50,927
Depreciation and amortization:
Depreciation and amortization	697	613	2,057	1,858
Total assets:
Total assets	551,914	488,867	551,914	488,867
Operating Segments | Public Sector Solutions
Net sales:
Net sales	162,000	177,359	373,801	433,698
Operating income (loss):
Operating income (loss)	3,165	7,082	(1,964)	4,677
Depreciation and amortization:
Depreciation and amortization	15	22	45	68
Total assets:
Total assets	123,520	90,437	123,520	90,437
Headquarters/Other
Operating income (loss):
Operating income (loss)	(5,758)	(4,324)	(12,533)	(11,744)
Depreciation and amortization:
Depreciation and amortization	2,962	2,323	7,756	7,811
Total assets:
Assets net of intercompany balance eliminations	(15,110)	(9,016)	(15,110)	(9,016)
Intersegment Elimination
Total assets:
Total assets	$ (60,802)	$ (36,077)	$ (60,802)	$ (36,077)