SEGMENT INFORMATION - Net Income, Assets and Certain Other Items of Segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net outside sales	$ 1,221,887	$ 920,333	$ 735,717
Cost of goods sold	1,019,418	768,054	617,214
Operating income	90,837	69,918	51,471
Identifiable assets	534,950	381,584	255,561
Depreciation and amortization	24,362	16,775	10,433
Manufacturing [Member]
Segment Reporting Information [Line Items]
Net outside sales	997,205	720,411	548,796
Distribution [Member]
Segment Reporting Information [Line Items]
Net outside sales	224,682	199,922	186,921
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Net outside sales	26,085	20,529	20,873
Intersegment Eliminations [Member] | Manufacturing [Member]
Segment Reporting Information [Line Items]
Net outside sales	23,187	17,964	18,356
Intersegment Eliminations [Member] | Distribution [Member]
Segment Reporting Information [Line Items]
Net outside sales	2,898	2,565	2,517
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net outside sales	1,247,972	940,862	756,590
Cost of goods sold	1,042,859	786,924	637,564
Operating income	122,106	91,372	66,497
Identifiable assets	482,928	351,982	218,147
Depreciation and amortization	21,655	14,663	8,647
Operating Segments [Member] | Manufacturing [Member]
Segment Reporting Information [Line Items]
Net outside sales	1,020,392	738,375	567,152
Cost of goods sold	853,596	616,038	477,189
Operating income	107,105	78,582	55,838
Identifiable assets	421,203	300,305	167,278
Depreciation and amortization	18,553	12,676	7,087
Operating Segments [Member] | Distribution [Member]
Segment Reporting Information [Line Items]
Net outside sales	227,580	202,487	189,438
Cost of goods sold	189,263	170,886	160,375
Operating income	15,001	12,790	10,659
Identifiable assets	61,725	51,677	50,869
Depreciation and amortization	$ 3,102	$ 1,987	$ 1,560